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Sample records for susceptibility suggesting antiferromagnetic

  1. Fidelity susceptibility study of quantum long-range antiferromagnetic Ising chain

    Science.gov (United States)

    Sun, Gaoyong

    2017-10-01

    We study the fidelity susceptibility of a quantum antiferromagnetic Ising chain with a long-range power-law interaction 1 /rα using the large-scale density matrix renormalization group method. We find that the critical adiabatic dimension μ =2 and the critical exponent of the correlation length ν =1 for arbitrary α >0 , indicating all quantum phase transitions are second-order Ising transitions. In addition, we numerically determine the complete phase diagram for 0 work will shed light on the nature of phase transitions in the quantum long-range antiferromagnetic Ising chain from a quantum information perspective.

  2. Perpendicular susceptibility and geometrical frustration in two-dimensional Ising antiferromagnets: Exact solutions

    Science.gov (United States)

    Muttalib, K. A.; Khatun, M.; Barry, J. H.

    2017-11-01

    Discovery of new materials and improved experimental as well as numerical techniques have led to a renewed interest in geometrically frustrated spin systems. However, there are very few exact results available that can provide a benchmark for comparison. In this work, we calculate exactly the perpendicular susceptibility χ⊥ for an Ising antiferromagnet with (i) nearest-neighbor pair interaction on a kagome lattice where strong frustration prevents long-range ordering and (ii) elementary triplet interactions on a kagome lattice which has no frustration but the system remains disordered down to zero temperature. By comparing with other known exact results with and without frustration, we propose that an appropriately temperature-scaled χ⊥ can be used as a quantitative measure of the degree of frustration in Ising spin systems.

  3. Genomic analysis suggests higher susceptibility of children to air pollution

    DEFF Research Database (Denmark)

    van Leeuwen, Danitsja M; Pedersen, Marie; Hendriksen, Peter J M

    2008-01-01

    Differences in biological responses to exposure to hazardous airborne substances between children and adults have been reported, suggesting children to be more susceptible. Aim of this study was to improve our understanding of differences in susceptibility in cancer risk associated with air...... pollution by comparing genome-wide gene expression profiles in peripheral blood of children and their parents. Gene expression analysis was performed in blood from children and parents living in two different regions in the Czech Republic with different levels of air pollution. Data were analyzed by two...... in relation to air pollution exposure at the transcriptome level. The findings underline the necessity of implementing environmental health policy measures specifically for protecting children's health....

  4. Magnetic susceptibility of the Kagome antiferromagnet ZnCu3(OH)6Cl2.

    Science.gov (United States)

    Rigol, Marcos; Singh, Rajiv R P

    2007-05-18

    We analyze the experimental data for the magnetic susceptibility of the material ZnCu3(OH)6Cl2 in terms of the Kagome Lattice Heisenberg model (KLHM), discussing possible role of impurity spins, dilution, exchange anisotropy, and both out-of-plane and in-plane Dzyloshinski-Moriya (DM) anisotropies, with explicit theoretical calculations using the numerical linked cluster method and exact diagonalization. The high-temperature experimental data are well described by the pure Heisenberg model with J=170 K. We show that the sudden upturn in the susceptibility around T=75 K is due to DM interactions. We also observe that at intermediate temperatures, below T=J, our calculated susceptibility for KLHM fits well with a power law T(-0.25).

  5. Association Analysis Suggests SOD2 as a Newly Identified Candidate Gene Associated With Leprosy Susceptibility.

    Science.gov (United States)

    Ramos, Geovana Brotto; Salomão, Heloisa; Francio, Angela Schneider; Fava, Vinícius Medeiros; Werneck, Renata Iani; Mira, Marcelo Távora

    2016-08-01

    Genetic studies have identified several genes and genomic regions contributing to the control of host susceptibility to leprosy. Here, we test variants of the positional and functional candidate gene SOD2 for association with leprosy in 2 independent population samples. Family-based analysis revealed an association between leprosy and allele G of marker rs295340 (P = .042) and borderline evidence of an association between leprosy and alleles C and A of markers rs4880 (P = .077) and rs5746136 (P = .071), respectively. Findings were validated in an independent case-control sample for markers rs295340 (P = .049) and rs4880 (P = .038). These results suggest SOD2 as a newly identified gene conferring susceptibility to leprosy. © The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.

  6. Antiferromagnetism in the organic conductor bis-tetramethyltetraselenafulvalene hexafluoroarsenate [(TMTSF)2AsF6]: Static magnetic susceptibility

    DEFF Research Database (Denmark)

    Mortensen, Kell; Tomkiewicz, Yaffa; Bechgaard, Klaus

    1982-01-01

    The anisotropy in the static magnetic susceptibility of bis-tetramethyltetraselenafulvalene hexafluoroarsenate [(TMTSF)2AsF6] has been investigated above and below the metal-to-insulator transition for a range of fields between 0.5 and 30 kG. The results are consistent with the expectations of a ...

  7. Antiferromagnetic spintronics

    Czech Academy of Sciences Publication Activity Database

    Jungwirth, Tomáš; Martí, Xavier; Wadley, P.; Wunderlich, Joerg

    2016-01-01

    Roč. 11, č. 3 (2016), 231-241 ISSN 1748-3387 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G EU Projects: European Commission(XE) 268066 - 0MSPIN Institutional support: RVO:68378271 Keywords : antiferromagnets * spintronics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 38.986, year: 2016

  8. Is working memory working against suggestion susceptibility? Results from extended version of DRM paradigm

    Directory of Open Access Journals (Sweden)

    Maciaszek Patrycja

    2016-04-01

    Full Text Available The paper investigates relationship between working memory efficiency, defined as the result of its’ processing & storage capacity (Oberauer et al., 2003 and the tendency to (1 create assosiative memory distortions (false memories, FM; (2 yield under the influence of external, suggesting factors. Both issues were examined using extended version of Deese-Roediger-McDermott procedure (1959, 1995, modified in order to meet the study demands. Suggestion was contained in an ostentatious feedback information the participants (N=88 received during the DRM procedure. Working memory (WM was measured by standardized tasks (n-back, Jaeggi et al., 2010; automatic-ospan, Unsworth et al., 2005. Study included 3 conditions, differing in the quality of suggestion (positive, negative or neutral. Participants were assigned into 3 groups, depending on results they achieved completing the WM tasks. Obtained results alongside the previously set hypothesis, revealed that (1 WM impacts individuals’ tendency to create false memories in DRM and (2 that the individuals showing higher rates in WM tasks are less willing to yield to suggestion compared to those with lesser ones. It also showed that the greater amount to shift (Gudjonsson, 2003, emerges under the negative suggestion condition (collating positive. Notwithstanding that the interaction effect did not achieve saliency, both analyzed factors (WM and suggesting content are considered as meaningful to explain memory suggestion susceptibility in presented study. Although, obtained results emphasize the crucial role of WM efficiency, that is believed to decide the magnitude of feedback that is influential in every subject. Therefore, issue demands further exploration.

  9. Contrasting patterns of coral bleaching susceptibility in 2010 suggest an adaptive response to thermal stress

    National Research Council Canada - National Science Library

    Guest, James R; Baird, Andrew H; Maynard, Jeffrey A; Muttaqin, Efin; Edwards, Alasdair J; Campbell, Stuart J; Yewdall, Katie; Affendi, Yang Amri; Chou, Loke Ming

    2012-01-01

    Coral bleaching events vary in severity, however, to date, the hierarchy of susceptibility to bleaching among coral taxa has been consistent over a broad geographic range and among bleaching episodes...

  10. Contrasting patterns of coral bleaching susceptibility in 2010 suggest an adaptive response to thermal stress.

    Science.gov (United States)

    Guest, James R; Baird, Andrew H; Maynard, Jeffrey A; Muttaqin, Efin; Edwards, Alasdair J; Campbell, Stuart J; Yewdall, Katie; Affendi, Yang Amri; Chou, Loke Ming

    2012-01-01

    Coral bleaching events vary in severity, however, to date, the hierarchy of susceptibility to bleaching among coral taxa has been consistent over a broad geographic range and among bleaching episodes. Here we examine the extent of spatial and temporal variation in thermal tolerance among scleractinian coral taxa and between locations during the 2010 thermally induced, large-scale bleaching event in South East Asia. Surveys to estimate the bleaching and mortality indices of coral genera were carried out at three locations with contrasting thermal and bleaching histories. Despite the magnitude of thermal stress being similar among locations in 2010, there was a remarkable contrast in the patterns of bleaching susceptibility. Comparisons of bleaching susceptibility within coral taxa and among locations revealed no significant differences between locations with similar thermal histories, but significant differences between locations with contrasting thermal histories (Friedman = 34.97; pBleaching was much less severe at locations that bleached during 1998, that had greater historical temperature variability and lower rates of warming. Remarkably, Acropora and Pocillopora, taxa that are typically highly susceptible, although among the most susceptible in Pulau Weh (Sumatra, Indonesia) where respectively, 94% and 87% of colonies died, were among the least susceptible in Singapore, where only 5% and 12% of colonies died. The pattern of susceptibility among coral genera documented here is unprecedented. A parsimonious explanation for these results is that coral populations that bleached during the last major warming event in 1998 have adapted and/or acclimatised to thermal stress. These data also lend support to the hypothesis that corals in regions subject to more variable temperature regimes are more resistant to thermal stress than those in less variable environments.

  11. A genome-wide scan of Ashkenazi Jewish Crohn's disease suggests novel susceptibility loci.

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    Eimear E Kenny

    Full Text Available Crohn's disease (CD is a complex disorder resulting from the interaction of intestinal microbiota with the host immune system in genetically susceptible individuals. The largest meta-analysis of genome-wide association to date identified 71 CD-susceptibility loci in individuals of European ancestry. An important epidemiological feature of CD is that it is 2-4 times more prevalent among individuals of Ashkenazi Jewish (AJ descent compared to non-Jewish Europeans (NJ. To explore genetic variation associated with CD in AJs, we conducted a genome-wide association study (GWAS by combining raw genotype data across 10 AJ cohorts consisting of 907 cases and 2,345 controls in the discovery stage, followed up by a replication study in 971 cases and 2,124 controls. We confirmed genome-wide significant associations of 9 known CD loci in AJs and replicated 3 additional loci with strong signal (p<5×10⁻⁶. Novel signals detected among AJs were mapped to chromosomes 5q21.1 (rs7705924, combined p = 2×10⁻⁸; combined odds ratio OR = 1.48, 2p15 (rs6545946, p = 7×10⁻⁹; OR = 1.16, 8q21.11 (rs12677663, p = 2×10⁻⁸; OR = 1.15, 10q26.3 (rs10734105, p = 3×10⁻⁸; OR = 1.27, and 11q12.1 (rs11229030, p = 8×10⁻⁹; OR = 1.15, implicating biologically plausible candidate genes, including RPL7, CPAMD8, PRG2, and PRG3. In all, the 16 replicated and newly discovered loci, in addition to the three coding NOD2 variants, accounted for 11.2% of the total genetic variance for CD risk in the AJ population. This study demonstrates the complementary value of genetic studies in the Ashkenazim.

  12. Nutrigenomics of high fat diet induced obesity in mice suggests relationships between susceptibility to fatty liver disease and the proteasome.

    Directory of Open Access Journals (Sweden)

    Helen Waller-Evans

    Full Text Available Nutritional factors play important roles in the etiology of obesity, type 2 diabetes mellitus and their complications through genotype x environment interactions. We have characterised molecular adaptation to high fat diet (HFD feeding in inbred mouse strains widely used in genetic and physiological studies. We carried out physiological tests, plasma lipid assays, obesity measures, liver histology, hepatic lipid measurements and liver genome-wide gene transcription profiling in C57BL/6J and BALB/c mice fed either a control or a high fat diet. The two strains showed marked susceptibility (C57BL/6J and relative resistance (BALB/c to HFD-induced insulin resistance and non alcoholic fatty liver disease (NAFLD. Global gene set enrichment analysis (GSEA of transcriptome data identified consistent patterns of expression of key genes (Srebf1, Stard4, Pnpla2, Ccnd1 and molecular pathways in the two strains, which may underlie homeostatic adaptations to dietary fat. Differential regulation of pathways, including the proteasome, the ubiquitin mediated proteolysis and PPAR signalling in fat fed C57BL/6J and BALB/c suggests that altered expression of underlying diet-responsive genes may be involved in contrasting nutrigenomic predisposition and resistance to insulin resistance and NAFLD in these models. Collectively, these data, which further demonstrate the impact of gene x environment interactions on gene expression regulations, contribute to improved knowledge of natural and pathogenic adaptive genomic regulations and molecular mechanisms associated with genetically determined susceptibility and resistance to metabolic diseases.

  13. Nutrigenomics of high fat diet induced obesity in mice suggests relationships between susceptibility to fatty liver disease and the proteasome.

    Science.gov (United States)

    Waller-Evans, Helen; Hue, Christophe; Fearnside, Jane; Rothwell, Alice R; Lockstone, Helen E; Caldérari, Sophie; Wilder, Steven P; Cazier, Jean-Baptiste; Scott, James; Gauguier, Dominique

    2013-01-01

    Nutritional factors play important roles in the etiology of obesity, type 2 diabetes mellitus and their complications through genotype x environment interactions. We have characterised molecular adaptation to high fat diet (HFD) feeding in inbred mouse strains widely used in genetic and physiological studies. We carried out physiological tests, plasma lipid assays, obesity measures, liver histology, hepatic lipid measurements and liver genome-wide gene transcription profiling in C57BL/6J and BALB/c mice fed either a control or a high fat diet. The two strains showed marked susceptibility (C57BL/6J) and relative resistance (BALB/c) to HFD-induced insulin resistance and non alcoholic fatty liver disease (NAFLD). Global gene set enrichment analysis (GSEA) of transcriptome data identified consistent patterns of expression of key genes (Srebf1, Stard4, Pnpla2, Ccnd1) and molecular pathways in the two strains, which may underlie homeostatic adaptations to dietary fat. Differential regulation of pathways, including the proteasome, the ubiquitin mediated proteolysis and PPAR signalling in fat fed C57BL/6J and BALB/c suggests that altered expression of underlying diet-responsive genes may be involved in contrasting nutrigenomic predisposition and resistance to insulin resistance and NAFLD in these models. Collectively, these data, which further demonstrate the impact of gene x environment interactions on gene expression regulations, contribute to improved knowledge of natural and pathogenic adaptive genomic regulations and molecular mechanisms associated with genetically determined susceptibility and resistance to metabolic diseases.

  14. Antiferromagnetic order and spin glass behavior in Dy{sub 2}CuIn{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Siouris, I.M., E-mail: jsiou@pme.duth.gr [Democritus University of Thrace (DUTH), Production and Management Engineering Department, Materials Laboratory, 67100 Xanthi (Greece); Kremer, R.K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Hoelzel, M. [Technische Universitaet Muenchen, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), 85748 Garching (Germany)

    2011-11-15

    The magnetic properties of the intermetallic compound Dy{sub 2}CuIn{sub 3} have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T{sub N}=19.5 K and an additional frequency dependent transition at T{sub ds}{approx}9 K. Neutron diffraction studies confirm the ordered transition at 19.5{+-}1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment {mu}=2.63(4){mu}{sub B}/Dy{sup 3+} parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions. - Highlights: > Dy{sub 2}CuIn{sub 3} is characterized by the dominance of antiferromagnetic (AF) interactions. > Geometric frustration and crystal field effects prevent the formation of the full magnetic moment on the Dy ions. > Two magnetic regimes are recognized: an AF state and a mixed AF-glassy state. > The antiferromagnetic structure of the compound has been determined.

  15. Thermodynamics of the antiferromagnetic Heisenberg model on the checkerboard lattice

    Science.gov (United States)

    Khatami, Ehsan; Rigol, Marcos

    2011-04-01

    Employing numerical linked-cluster expansions (NLCEs) along with exact diagonalizations of finite clusters with periodic boundary condition, we study the energy, specific heat, entropy, and various susceptibilities of the antiferromagnetic Heisenberg model on the checkerboard lattice. NLCEs, combined with extrapolation techniques, allow us to access temperatures much lower than those accessible to exact diagonalization and other series expansions. We show that the high-temperature peak in specific heat decreases as the frustration increases, consistent with the large amount of unquenched entropy in the region around maximum classical frustration, where the nearest-neighbor and next-nearest-neighbor exchange interactions (J and J', respectively) have the same strength, and with the formation of a second peak at lower temperatures. The staggered susceptibility shows a change of character when J' increases beyond 0.75J, implying the disappearance of the antiferromagnetic order at low temperatures. For J'=4J, in the limit of weakly coupled crossed chains, we find large susceptibilities for stripe and Néel order with Q=(π/2,π/2) at intermediate temperatures. Other magnetic and bond orderings, such as a plaquette valence-bond solid and a crossed-dimer order suggested by previous studies, are also investigated.

  16. Topological crystalline antiferromagnetic state in tetragonal FeS

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    Hao, Ningning; Zheng, Fawei; Zhang, Ping; Shen, Shun-Qing

    2017-10-01

    Integration between magnetism and topology is an exotic phenomenon in condensed-matter physics. Here, we propose an exotic phase named topological crystalline antiferromagnetic state, in which antiferromagnetism intrinsically integrates with nontrivial topology, and we suggest such a state can be realized in tetragonal FeS. A combination of first-principles calculations and symmetry analyses shows that the topological crystalline antiferromagnetic state arises from band reconstruction induced by pair checkerboard antiferromagnetic order together with band-gap opening induced by intrinsic spin-orbit coupling in tetragonal FeS. The topological crystalline antiferromagnetic state is protected by the product of fractional translation symmetry, mirror symmetry, and time-reversal symmetry, and presents some unique features. In contrast to strong topological insulators, the topological robustness is surface dependent. These findings indicate that nontrivial topological states could emerge in pure antiferromagnetic materials, which sheds new light on potential applications of topological properties in fast-developing antiferromagnetic spintronics.

  17. New Findings in eNOS gene and Thalidomide Embryopathy Suggest pre-transcriptional effect variants as susceptibility factors.

    Science.gov (United States)

    Kowalski, Thayne Woycinck; Fraga, Lucas Rosa; Tovo-Rodrigues, Luciana; Sanseverino, Maria Teresa Vieira; Hutz, Mara Helena; Schuler-Faccini, Lavínia; Vianna, Fernanda Sales Luiz

    2016-03-23

    Antiangiogenic properties of thalidomide have created an interest in the use of the drug in treatment of cancer. However, thalidomide is responsible for thalidomide embryopathy (TE). A lack of knowledge regarding the mechanisms of thalidomide teratogenesis acts as a barrier in the aim to synthesize a safer analogue of thalidomide. Recently, our group detected a higher frequency of alleles that impair the pro-angiogenic mechanisms of endothelial nitric oxide synthase (eNOS), coded by the NOS3 gene. In this study we evaluated variable number tandem repeats (VNTR) functional polymorphism in intron 4 of NOS3 in individuals with TE (38) and Brazilians without congenital anomalies (136). Haplotypes were estimated for this VNTR with previously analyzed polymorphisms, rs2070744 (-786C > T) and rs1799983 (894T > G), in promoter region and exon 7, respectively. Haplotypic distribution was different between the groups (p = 0.007). Alleles -786C (rs2070744) and 4b (VNTR), associated with decreased NOS3 expression, presented in higher frequency in TE individuals (p = 0.018; OR = 2.57; IC = 1.2-5.8). This association was not identified with polymorphism 894T > G (p = 0.079), which influences eNOS enzymatic activity. These results suggest variants in NOS3, with pre-transcriptional effects as susceptibility factors, influencing the risk TE development. This finding generates insight for a new approach to research that pursues a safer analogue.

  18. Nanoparticles of antiferromagnetic materials

    DEFF Research Database (Denmark)

    Madsen, Daniel Esmarch

    2008-01-01

    I denne Ph.D. afhandling studeres forskellige egenskaber ved antiferromagnetiske nanopartikler. I en ideel antiferromagnet er spinnene orienteret således at der ikke er et resulterende magnetisk moment. I nanopartikler af antiferromagnetiske materialer er denne kompensation på grund af forskellig...

  19. Antiferromagnetic spin-orbitronics

    KAUST Repository

    Manchon, Aurelien

    2015-05-01

    Antiferromagnets have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves [1]. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties mostly considered from a fundamental perspective.

  20. On the interpretation of magnetization data for antiferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Madsen, Daniel Esmarch; Mørup, Steen; Hansen, Mikkel Fougt

    2006-01-01

    We have investigated the influence of anisotropy on the magnetization curves of antiferromagnetic nanoparticles. We show that if such curves are analyzed in a conventional way, i.e. using a Langevin function in combination with a linear term, this usually results in good quality fits......, but with an apparent temperature dependence of parameters such as the magnetic moment per particle and the antiferromagnetic susceptibility. In order to avoid the problems associated with anisotropy as well as volume/moment distributions we propose that the initial susceptibility is used when analyzing the temperature...... dependence of the magnetic moment....

  1. Allergic rhinitis - a total genome-scan for susceptibility genes suggests a locus on chromosome 4q24-q27

    DEFF Research Database (Denmark)

    Haagerup, A; Bjerke, T; Schøitz, P O

    2001-01-01

    definition of both clinical allergic rhinitis and confirmed specific allergy were chosen. Thirty-three affected sib-pair families qualified for the scan that was undertaken using 446 microsatellite markers. Non-parametric linkage results were obtained from MAPMAKER/SIBS computer program. The study revealed...... one major candidate region on chromosome 4q24-q27 (LOD=2.83) and eight minor candidate regions 2q12-q33, 3q13, 4p15-q12, 5q13-q15, 6p24-p23, 12p13, 22q13, and Xp21 (LOD=1.04-1.63) likely to contain susceptibility genes for allergic rhinitis. Our findings did not support a previous report of linkage...... of allergic rhinitis to chromosome 12q14-q24 but they added positive evidence to the asthma and atopy candidate regions 2q33 and 6p23. Further identification of the specific genes involved in allergic rhinitis will give opportunities for improved diagnosis and treatment....

  2. Antiferromagnetic transition in graphene functionalized with nitroaniline

    Science.gov (United States)

    Komlev, Anton A.; Makarova, Tatiana L.; Lahderanta, Erkki; Semenikhin, Petr Valeryevich; Veinger, Anatoly I.; Kochman, Igor V.; Magnani, Giacomo; Bertoni, Giovanni; Pontiroli, Daniele; Ricco, Mauro

    2017-07-01

    Magnetic properties of graphene nanostructures functionalized with aromatic radicals were investigated by electron spin resonance (ESR) and superconducting quantum interference device (SQUID) techniques. Three types of functionalized graphene samples were investigated (functionalization was performed by 4-bromoaniline, 4-nitroaniline, or 4-chloroaniline). According to SQUID measurements, in case of functionalization by nitroaniline, sharp change in temperature dependence of magnetic susceptibility was observed near 120 K. Such behavior was explained as antiferromagnetic ordering. The same but more extended effect was observed in ESR measurements below 160 K. In the ESR measurements, only one resonance line with g-factor equal to 2.003 was observed. Based on the temperature dependencies of spin concentration and resonance position and intensity, the effect was explained as antiferromagnetic ordering along the extended defects on the basal planes of the graphene.

  3. The association of AKNA gene polymorphisms with knee osteoarthritis suggests the relevance of this immune response regulator in the disease genetic susceptibility.

    Science.gov (United States)

    Martínez-Nava, Gabriela Angélica; Fernández-Torres, Javier; Martínez-Flores, Karina; Zamudio-Cuevas, Yessica; Clavijo-Cornejo, Denise; Espinosa-Morales, Rolando; Lozada, Carlos A; Gutierrez, Marwin; Granados, Julio; Pineda, Carlos; Madrid-Marina, Vicente; López-Reyes, Alberto

    2018-01-24

    Recent studies have identified AKNA as a potential susceptibility gene for several inflammatory diseases. Here, we aimed to assess the potential association of AKNA polymorphisms with knee osteoarthritis (KOA) susceptibility in a Mexican population, following STREGA recommendations. From a DNA bank of 181 KOA patients and 140 healthy controls, two AKNA SNPs were genotyped using TaqMan probes. The association between KOA susceptibility and AKNA polymorphisms genotypes was evaluated by multivariated logistic regression analysis. Information regarding patients' inflammatory biomarkers levels was obtained and their association with AKNA polymorphisms genotypes was assessed by lineal regression. We found a positive association with the recessive inheritance model of both AKNA polymorphisms (A/A genotype for both) and KOA susceptibility adjusting by age, body mass index (BMI), gender and place of birth (OR = 2.48, 95% CI 1.09-5.65 for rs10817595 polymorphism; and OR = 4.96; 95% CI 2.421-10.2 for rs3748176 polymorphism). Additionally these associations were also seen after stratifying patients by KOA severity and age. Furthermore the total leukocyte count was positively associated with rs10817595 AKNA polymorphism (β = 1.39; 95% CI 0.44-2.34) adjusting by age, BMI, gender, place of birth and disease severity. We suggest that regulatory and coding polymorphisms of the inflammatory modulator gene AKNA can influence the development of KOA. Further structural and functional studies might reveal the role of AKNA in OA and other rheumatic diseases.

  4. Crystallographic Studies of Prion Protein (PrP) Segments Suggest How Structural Changes Encoded by Polymorphism at Residue 129 Modulate Susceptibility to Human Prion Disease

    Energy Technology Data Exchange (ETDEWEB)

    Apostol, Marcin I.; Sawaya, Michael R.; Cascio, Duilio; Eisenberg, David (UCLA)

    2010-09-23

    A single nucleotide polymorphism (SNP) in codon 129 of the human prion gene, leading to a change from methionine to valine at residue 129 of prion protein (PrP), has been shown to be a determinant in the susceptibility to prion disease. However, the molecular basis of this effect remains unexplained. In the current study, we determined crystal structures of prion segments having either Met or Val at residue 129. These 6-residue segments of PrP centered on residue 129 are 'steric zippers,' pairs of interacting {beta}-sheets. Both structures of these 'homozygous steric zippers' reveal direct intermolecular interactions between Met or Val in one sheet and the identical residue in the mating sheet. These two structures, plus a structure-based model of the heterozygous Met-Val steric zipper, suggest an explanation for the previously observed effects of this locus on prion disease susceptibility and progression.

  5. Antiferromagnetic spin Seebeck effect.

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-03

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  6. Antiferromagnetic Spin Seebeck Effect.

    Science.gov (United States)

    Wu, Stephen M; Zhang, Wei; Kc, Amit; Borisov, Pavel; Pearson, John E; Jiang, J Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-04

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30  nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9  T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  7. Electrical switching of an antiferromagnet

    Science.gov (United States)

    Wadley, P.; Howells, B.; Železný, J.; Andrews, C.; Hills, V.; Campion, R. P.; Novák, V.; Olejník, K.; Maccherozzi, F.; Dhesi, S. S.; Martin, S. Y.; Wagner, T.; Wunderlich, J.; Freimuth, F.; Mokrousov, Y.; Kuneš, J.; Chauhan, J. S.; Grzybowski, M. J.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Jungwirth, T.

    2016-02-01

    Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 106 ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.

  8. Genome-wide linkage study suggests a susceptibility locus for isolated bilateral microtia on 4p15.32-4p16.2.

    Directory of Open Access Journals (Sweden)

    Xin Li

    Full Text Available Microtia is a congenital deformity where the external ear is underdeveloped. Genetic investigations have identified many susceptibility genes of microtia-related syndromes. However, no causal genes were reported for isolated microtia, the main form of microtia. We conducted a genome-wide linkage analysis on a 5-generation Chinese pedigree with isolated bilateral microtia. We identified a suggestive linkage locus on 4p15.32-4p16.2 with parametric LOD score of 2.70 and nonparametric linkage score (Zmean of 12.28 (simulated occurrence per genome scan equal to 0.46 and 0.47, respectively. Haplotype reconstruction analysis of the 4p15.32-4p16.2 region further confined the linkage signal to a 10-Mb segment located between rs12505562 and rs12649803 (9.65-30.24 cM; 5.54-15.58 Mb. Various human organ developmental genes reside in this 10-Mb susceptibility region, such as EVC, EVC2, SLC2A9, NKX3-2, and HMX1. The coding regions of three genes, EVC known for cartilage development and NKX3-2, HMX1 involved in microtia, were selected for sequencing with 5 individuals from the pedigree. Of the 38 identified sequence variants, none segregates along with the disease phenotype. Other genes or DNA sequences of the 10-Mb region warrant for further investigation. In conclusion, we report a susceptibility locus of isolated microtia, and this finding will encourage future studies on the genetic basis of ear deformity.

  9. Quarks, Gluons and Frustrated Antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Weinstein, Marvin

    1999-10-05

    The Contractor Renormalization Group method (CORE) is used to establish the equivalence of various Hamiltonian free fermion theories and a class of generalized frustrated antiferromagnets. In particular, after a detailed discussion of a simple example, it is argued that a generalized frustrated SU(3) antiferromagnet whose single-site states have the quantum numbers of mesons and baryons is equivalent to a theory of free massless quarks. Furthermore, it is argued that for slight modification of the couplings which define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory of quarks interacting with color gauge-fields.

  10. Tetrahedrally coordinated half-metallic antiferromagnets

    Science.gov (United States)

    Nakao, Masao

    2006-11-01

    We explore the electronic structures of transition-metal-based chalcopyrites TMX2 ( X=S , Se, and Te) to establish a concept of half-metallic antiferromagnets (HM-AFM’s) within the class of tetrahedrally coordinated ternary systems. Using a full-potential muffin-tin approach and the spin-polarized density functional method, we find two series of HM-AFM’s: CrFeX2 and VCoX2 , where two constituent magnetic ions in a unit cell have antialigned local moments that cancel exactly by virtue of the integer filling of one spin channel. The bonding nature is interpreted in terms of the “ghost-bond-orbital model”; the T - X bonds are covalent while the M - X bonds are ionic, suggesting the magnetic interaction in each bond is due to ferromagnetic double exchange and antiferromagnetic superexchange, respectively, in the conventional scheme.

  11. Superconducting Vortex with Antiferromagnetic Core

    Energy Technology Data Exchange (ETDEWEB)

    Arovas, D.P. [Department of Physics, University of California at San Diego, La Jolla, California 92093 (United States); Berlinsky, A.J.; Kallin, C.; Zhang, S. [Department of Physics, Stanford University, Stanford, California 94305 (United States)

    1997-10-01

    We show that a superconducting vortex in underdoped high T{sub c} superconductors could have an antiferromagnetic core. This type of vortex configuration arises as a topological solution in the recently constructed SO(5) nonlinear {sigma} model and in Landau-Ginzburg theory with competing antiferromagnetic and superconducting order parameters. Experimental detection of this type of vortex by muon spin resonance and neutron scattering is proposed. {copyright} {ital 1997} {ital The American Physical Society}

  12. Exchange anisotropy of ferromagnetic/antiferromagnetic bilayers intrinsic magnetic anisotropy of antiferromagnetic layer and single spin ensemble model

    CERN Document Server

    Tsunoda, M

    2002-01-01

    The origin of the magnetic anisotropy of the antiferromagnetic (AF) layer and the role of it in the magnetization process of exchange coupled ferromagnetic/antiferromagnetic bilayers are discussed. Through the magnetic torque analysis of a pseudo-single crystalline Ni-Fe/Mn-Ni bilayer and a polycrystalline Ni-Fe/Mn-Ir bilayer, the magnetocrystalline anisotropy of the antiferromagnet is strongly suggested to be the origin of the magnetic anisotropy of the antiferromagnetic (AF) layer. The single spin ensemble model is newly introduced for polycrystalline bilayers, taking into account the two-dimensionally random distribution of the magnetic anisotropy axes of the AF grains. The mechanism of a well-known experimental fact, the reversible induction of the exchange anisotropy along desirable directions by field cooling procedure, is successfully elucidated with the new model.

  13. Magnetic properties of a quasi-one-dimensional S=1/2 antiferromagnet: Copper benzoate

    DEFF Research Database (Denmark)

    Dender, D.C.; Davidovic, D.; Reich, D.H.

    1996-01-01

    We use magnetic susceptibility and inelastic neutron scattering measurements to show that copper benzoate, Cu(C6D5COO)(2) . 3D(2)O, is a quasi-one-dimensional S=1/2 antiferromagnet with an exchange constant J=1.57 meV Below T=0.8 K a ferromagnetic contribution to the susceptibility marks the onset...

  14. Electrical switching of an antiferromagnet

    Science.gov (United States)

    Jungwirth, Tomas

    Louis Néel pointed out in his Nobel lecture that while abundant and interesting from theoretical viewpoint, antiferromagnets did not seem to have any applications. Indeed, the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization make antiferromagnets hard to control by tools common in ferromagnets. Strong coupling would be achieved if the externally generated field had a sign alternating on the scale of a lattice constant at which moments alternate in AFMs. However, generating such a field has been regarded unfeasible, hindering the research and applications of these abundant magnetic materials. We have recently predicted that relativistic quantum mechanics may offer staggered current induced fields with the sign alternating within the magnetic unit cell which can facilitate a reversible switching of an antiferromagnet by applying electrical currents with comparable efficiency to ferromagnets. Among suitable materials is a high Néel temperature antiferromagnet, tetragonal-phase CuMnAs, which we have recently synthesized in the form of single-crystal epilayers structurally compatible with common semiconductors. We demonstrate electrical writing and read-out, combined with the insensitivity to magnetic field perturbations, in a proof-of-concept antiferromagnetic memory device. We acknowledge support from European Research Council Advanced Grant No. 268066.

  15. GWAS of follicular lymphoma reveals allelic heterogeneity at 6p21.32 and suggests shared genetic susceptibility with diffuse large B-cell lymphoma.

    Directory of Open Access Journals (Sweden)

    Karin E Smedby

    2011-04-01

    Full Text Available Non-Hodgkin lymphoma (NHL represents a diverse group of hematological malignancies, of which follicular lymphoma (FL is a prevalent subtype. A previous genome-wide association study has established a marker, rs10484561 in the human leukocyte antigen (HLA class II region on 6p21.32 associated with increased FL risk. Here, in a three-stage genome-wide association study, starting with a genome-wide scan of 379 FL cases and 791 controls followed by validation in 1,049 cases and 5,790 controls, we identified a second independent FL-associated locus on 6p21.32, rs2647012 (OR(combined  = 0.64, P(combined  = 2 × 10(-21 located 962 bp away from rs10484561 (r(2<0.1 in controls. After mutual adjustment, the associations at the two SNPs remained genome-wide significant (rs2647012:OR(adjusted  = 0.70, P(adjusted  =  4 × 10(-12; rs10484561:OR(adjusted  = 1.64, P(adjusted  = 5 × 10(-15. Haplotype and coalescence analyses indicated that rs2647012 arose on an evolutionarily distinct haplotype from that of rs10484561 and tags a novel allele with an opposite (protective effect on FL risk. Moreover, in a follow-up analysis of the top 6 FL-associated SNPs in 4,449 cases of other NHL subtypes, rs10484561 was associated with risk of diffuse large B-cell lymphoma (OR(combined  = 1.36, P(combined  =  1.4 × 10(-7. Our results reveal the presence of allelic heterogeneity within the HLA class II region influencing FL susceptibility and indicate a possible shared genetic etiology with diffuse large B-cell lymphoma. These findings suggest that the HLA class II region plays a complex yet important role in NHL.

  16. Low Field Magnetic and Thermal Hysteresis in Antiferromagnetic Dysprosium

    Directory of Open Access Journals (Sweden)

    Iuliia Liubimova

    2017-06-01

    Full Text Available Magnetic and thermal hysteresis (difference in magnetic properties on cooling and heating have been studied in polycrystalline Dy (dysprosium between 80 and 250 K using measurements of the reversible Villari effect and alternating current (AC susceptibility. We argue that measurement of the reversible Villari effect in the antiferromagnetic phase is a more sensitive method to detect magnetic hysteresis than the registration of conventional B(H loops. We found that the Villari point, recently reported in the antiferromagnetic phase of Dy at 166 K, controls the essential features of magnetic hysteresis and AC susceptibility on heating from the ferromagnetic state: (i thermal hysteresis in AC susceptibility and in the reversible Villari effect disappears abruptly at the temperature of the Villari point; (ii the imaginary part of AC susceptibility is strongly frequency dependent, but only up to the temperature of the Villari point; (iii the imaginary part of the susceptibility drops sharply also at the Villari point. We attribute these effects observed at the Villari point to the disappearance of the residual ferromagnetic phase. The strong influence of the Villari point on several magnetic properties allows this temperature to be ranked almost as important as the Curie and Néel temperatures in Dy and likely also for other rare earth elements and their alloys.

  17. How to manipulate magnetic states of antiferromagnets

    Science.gov (United States)

    Song, Cheng; You, Yunfeng; Chen, Xianzhe; Zhou, Xiaofeng; Wang, Yuyan; Pan, Feng

    2018-03-01

    Antiferromagnetic materials, which have drawn considerable attention recently, have fascinating features: they are robust against perturbation, produce no stray fields, and exhibit ultrafast dynamics. Discerning how to efficiently manipulate the magnetic state of an antiferromagnet is key to the development of antiferromagnetic spintronics. In this review, we introduce four main methods (magnetic, strain, electrical, and optical) to mediate the magnetic states and elaborate on intrinsic origins of different antiferromagnetic materials. Magnetic control includes a strong magnetic field, exchange bias, and field cooling, which are traditional and basic. Strain control involves the magnetic anisotropy effect or metamagnetic transition. Electrical control can be divided into two parts, electric field and electric current, both of which are convenient for practical applications. Optical control includes thermal and electronic excitation, an inertia-driven mechanism, and terahertz laser control, with the potential for ultrafast antiferromagnetic manipulation. This review sheds light on effective usage of antiferromagnets and provides a new perspective on antiferromagnetic spintronics.

  18. Focused issue on antiferromagnetic spintronics: An overview (Part of a collection of reviews on antiferromagnetic spintronics)

    KAUST Repository

    Jungwirth, T.

    2017-05-30

    This focused issue attempts to provide a comprehensive introduction into the field of antiferromagnetic spintronics. Apart from the brief overview below, it features five review articles. The intention is to cover in a coherent and complementary way key physical aspects of the antiferromagnetic spintronics research. These range from microelectronic memory devices and optical manipulation and detection of antiferromagnetic spins, to the fundamentals of antiferromagnetic dynamics in uniform or spin-textured systems, and to the interplay of antiferromagnetic spintronics with topological phenomena. The antiferromagnetic ordering can take a number of forms including fully compensated collinear, non-collinear, and non-coplanar magnetic lattices, compensated and uncompensated ferrimagnets, or metamagnetic materials hosting an antiferromagnetic to ferromagnetic phase transition. Apart from the variety of distinct magnetic crystal structures, the focused issue also encompasses spintronic phenomena and devices studied in antiferromagnet/ferromagnet heterostructures and in synthetic antiferromagnets.

  19. Magnetic excitations in a new anisotropic kagome antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Robert, J. [Laboratoire Louis Neel, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Simonet, V. [Laboratoire Louis Neel, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France)]. E-mail: simonet@grenoble.cnrs.fr; Canals, B. [Laboratoire Louis Neel, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Ballou, R. [Laboratoire Louis Neel, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Bordet, P. [Laboratoire de Cristallographie, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Gelard, I. [Laboratoire de Cristallographie, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Ibanez, A. [Laboratoire de Cristallographie, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Lejay, P. [Centre de Recherches des Tres Basses Temperatures, CNRS, B.P. 166, 38 042 Grenoble Cedex 9 (France); Ollivier, J. [Institut Laue-Langevin, B.P. 154, 38042 Grenoble Cedex (France); Stunault, A. [Institut Laue-Langevin, B.P. 154, 38042 Grenoble Cedex (France)

    2006-11-15

    The Nd-langasite compound contains planes of magnetic Nd{sup 3+} ions on a lattice topologically equivalent to a kagome net. The magnetic susceptibility does not reveal any signature of long-range ordering down to 2K but rather a correlated paramagnetism with significant antiferromagnetic interactions between the Nd and a single-ion anisotropy due to crystal field effect. Inelastic neutron scattering on Nd-langasite powder and single crystal allowed to probe its very peculiar low temperature dynamical magnetic correlations. They present unusual dispersive features and are broadly localized in wave vector Q revealing a structure factor associated to characteristics short-range correlations between the magnetic atoms. From comparison with theoretical calculations, these results are interpreted as a possible experimental observation of a spin-liquid state in an anisotropic kagome antiferromagnet.

  20. Spin structures in antiferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Brok, Erik

    in plate-shaped NiO nanoparticles with thicknesses down to 2.0 nm is investigated with the XY Z-neutron polarisation analysis technique. This provides an effective way of separating the different scattering contributions (magnetic, nuclear and spin incoherent), and thus significantly improve the earlier......In this thesis magnetic structures of antiferromagnetic nanoparticles are studied as a function of particle size and aggregation. In nanoparticles the magnetic structure can be different from that of the corresponding bulk system due to the following reasons: a) a significant surface contribution...... to the magnetic anisotropy, b) the low symmetry environment of surface atoms or defects in the interior of particles leading to non collinear spin structures, and c) exchange interactions between neighbouring particles. Determining the spin structures of antiferromagnetic particles is difficult, however...

  1. Possible Itinerant-Electron Canted Antiferromagnetism in Tetragonal Antiperovskite Cr3AsN

    Science.gov (United States)

    Waki, Takeshi; Takao, Kenta; Tabata, Yoshikazu; Ohta, Hiroto; Yajima, Takeshi; Hiroi, Zenji; Nakamura, Hiroyuki

    2017-10-01

    We studied the magnetic, transport, and structural properties of the tetragonally distorted antiperovskite nitride Cr3AsN. A ferromagnetic-like increase in magnetic susceptibility below the magnetic transition temperature Tm = 255 K is reported for the first time. This magnetic transition is of the second order and not associated with a structural transition, unlike that in Mn-based antiperovskites. Although the observed spontaneous moment of 0.062 μB/Cr at the lowest temperature is very small, the reduction in the magnetic scattering in resistivity and spontaneous magnetostriction below Tm indicate the existence of a magnetic moment larger than the observed spontaneous magnetization. Zero-field 53Cr and 75As NMR results below Tm reveal the presence of a static moment of ˜0.5 μB at the Cr sites and a hyperfine field lying in the c-plane at the As site. Macroscopic and microscopic observations suggest the incomplete compensation of antiferromagnetically coupled moments. Canted antiferromagnetism is proposed for the itinerant-electron magnet.

  2. Anti-Ferromagnetic Condensate in Yang-Mills Theory

    OpenAIRE

    Fingberg, Jochen; Polonyi, Janos

    1996-01-01

    SU(2) gauge theory with competing interactions is shown to possess a rich phase structure with anti-ferromagnetic vacua. It is argued that the phase boundaries persist in the weak coupling limit suggesting the existence of different renormalized continuum theories for QCD.

  3. μ SR insight into the impurity problem in quantum kagome antiferromagnets

    Science.gov (United States)

    Gomilšek, M.; Klanjšek, M.; Pregelj, M.; Luetkens, H.; Li, Y.; Zhang, Q. M.; Zorko, A.

    2016-07-01

    Impurities, which are unavoidable in real materials, may play an important role in the magnetism of frustrated spin systems with a spin-liquid ground state. We address the impurity issue in quantum kagome antiferromagnets by investigating ZnCu3(OH) 6SO4 (Zn-brochantite) by means of muon spin spectroscopy. We show that muons dominantly couple to impurities, originating from Cu-Zn intersite disorder, and that the impurity spins are highly correlated with the kagome spins, allowing us to probe the host kagome physics via a Kondo-like effect. The low-temperature plateau in the impurity susceptibility suggests that the kagome spin-liquid ground state is gapless. The corresponding spin fluctuations exhibit an unconventional spectral density and a nontrivial field dependence.

  4. The peak effect (PE) region of the antiferromagnetic two layer Ising nanographene

    Science.gov (United States)

    Şarlı, Numan; Akbudak, Salih; Ellialtıoğlu, Mehmet Recai

    2014-11-01

    In this work, the magnetic properties of the ferromagnetic and antiferromagnetic two layer spin-1/2 Ising nanographene systems are investigated within the effective field theory. We find that the magnetizations and the hysteresis behaviors of the central graphene atoms are similar to those of the edge graphene atoms in the ferromagnetic case. But, they are quite different in the antiferromagnetic case. The antiferromagnetic central graphene atoms exhibit type II superconductivity and they have triple hysteresis loop. The peak effect (PE) region is observed on the hysteresis curves of the antiferromagnetic Ising nanographene system. Therefore, we suggest that there is a strong relationship between the antiferromagnetism and the peak effect. Our results are in agreement with some experimental works in recent literature.

  5. Whole exome sequencing suggests much of non-BRCA1/BRCA2 familial breast cancer is due to moderate and low penetrance susceptibility alleles.

    Directory of Open Access Journals (Sweden)

    Francisco Javier Gracia-Aznarez

    Full Text Available The identification of the two most prevalent susceptibility genes in breast cancer, BRCA1 and BRCA2, was the beginning of a sustained effort to uncover new genes explaining the missing heritability in this disease. Today, additional high, moderate and low penetrance genes have been identified in breast cancer, such as P53, PTEN, STK11, PALB2 or ATM, globally accounting for around 35 percent of the familial cases. In the present study we used massively parallel sequencing to analyze 7 BRCA1/BRCA2 negative families, each having at least 6 affected women with breast cancer (between 6 and 10 diagnosed under the age of 60 across generations. After extensive filtering, Sanger sequencing validation and co-segregation studies, variants were prioritized through either control-population studies, including up to 750 healthy individuals, or case-control assays comprising approximately 5300 samples. As a result, a known moderate susceptibility indel variant (CHEK2 1100delC and a catalogue of 11 rare variants presenting signs of association with breast cancer were identified. All the affected genes are involved in important cellular mechanisms like DNA repair, cell proliferation and survival or cell cycle regulation. This study highlights the need to investigate the role of rare variants in familial cancer development by means of novel high throughput analysis strategies optimized for genetically heterogeneous scenarios. Even considering the intrinsic limitations of exome resequencing studies, our findings support the hypothesis that the majority of non-BRCA1/BRCA2 breast cancer families might be explained by the action of moderate and/or low penetrance susceptibility alleles.

  6. Whole exome sequencing suggests much of non-BRCA1/BRCA2 familial breast cancer is due to moderate and low penetrance susceptibility alleles.

    Science.gov (United States)

    Gracia-Aznarez, Francisco Javier; Fernandez, Victoria; Pita, Guillermo; Peterlongo, Paolo; Dominguez, Orlando; de la Hoya, Miguel; Duran, Mercedes; Osorio, Ana; Moreno, Leticia; Gonzalez-Neira, Anna; Rosa-Rosa, Juan Manuel; Sinilnikova, Olga; Mazoyer, Sylvie; Hopper, John; Lazaro, Conchi; Southey, Melissa; Odefrey, Fabrice; Manoukian, Siranoush; Catucci, Irene; Caldes, Trinidad; Lynch, Henry T; Hilbers, Florentine S M; van Asperen, Christi J; Vasen, Hans F A; Goldgar, David; Radice, Paolo; Devilee, Peter; Benitez, Javier

    2013-01-01

    The identification of the two most prevalent susceptibility genes in breast cancer, BRCA1 and BRCA2, was the beginning of a sustained effort to uncover new genes explaining the missing heritability in this disease. Today, additional high, moderate and low penetrance genes have been identified in breast cancer, such as P53, PTEN, STK11, PALB2 or ATM, globally accounting for around 35 percent of the familial cases. In the present study we used massively parallel sequencing to analyze 7 BRCA1/BRCA2 negative families, each having at least 6 affected women with breast cancer (between 6 and 10) diagnosed under the age of 60 across generations. After extensive filtering, Sanger sequencing validation and co-segregation studies, variants were prioritized through either control-population studies, including up to 750 healthy individuals, or case-control assays comprising approximately 5300 samples. As a result, a known moderate susceptibility indel variant (CHEK2 1100delC) and a catalogue of 11 rare variants presenting signs of association with breast cancer were identified. All the affected genes are involved in important cellular mechanisms like DNA repair, cell proliferation and survival or cell cycle regulation. This study highlights the need to investigate the role of rare variants in familial cancer development by means of novel high throughput analysis strategies optimized for genetically heterogeneous scenarios. Even considering the intrinsic limitations of exome resequencing studies, our findings support the hypothesis that the majority of non-BRCA1/BRCA2 breast cancer families might be explained by the action of moderate and/or low penetrance susceptibility alleles.

  7. Spin diffusion and torques in disordered antiferromagnets

    KAUST Repository

    Manchon, Aurelien

    2017-02-01

    We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.

  8. Antiferromagnetic exchange spring as the reason of exchange bias training effect

    Science.gov (United States)

    Dobrynin, A. N.; Maccherozzi, F.; Dhesi, S. S.; Fan, R.; Bencok, P.; Steadman, P.

    2014-07-01

    We observe recovery of the exchange bias training effect in a Co/CoO bilayer after warming the sample up to the blocking temperature and cooling it back to a low measuring temperature in zero magnetic field. Variation of the magnitude of X-ray magnetic linear dichroism in the sample for the system in the high unidirectional anisotropy state (after field cooling) and in the low unidirectional anisotropy state (after training) suggests rearrangement of antiferromagnetic structure during the initial field cycling in exchange biased state. Our results suggest formation of an antiferromagnetic exchange spring at the frustrated ferromagnetic-antiferromagnetic interface being the reason of the training effect.

  9. Critical Behaviour of a Two-Dimensional Random Antiferromagnet

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.

    1976-01-01

    A neutron scattering study of the order parameter, correlation length and staggered susceptibility of the two-dimensional random antiferromagnet Rb2Mn0.5Ni0.5F4 is reported. The system is found to exhibit a well-defined phase transition with critical exponents identical to those of the isomorphou...... pure materials K2NiF4 and K2MnF4. Thus, in these systems, which have the asymptotic critical behaviour of the two-dimensional Ising model, randomness has no measurable effect on the phase-transition behaviour....

  10. Magnetic structure of the quasi-two-dimensional antiferromagnet NiPS3

    Science.gov (United States)

    Wildes, A. R.; Simonet, V.; Ressouche, E.; McIntyre, G. J.; Avdeev, M.; Suard, E.; Kimber, S. A. J.; Lançon, D.; Pepe, G.; Moubaraki, B.; Hicks, T. J.

    2015-12-01

    The magnetic structure of the quasi-two-dimensional antiferromagnet NiPS3 has been determined by magnetometry and a variety of neutron diffraction techniques. The experiments show that the samples must be carefully handled, as gluing influences the magnetometry measurements while preferred orientation complicates the interpretation of powder diffraction measurements. Our global set of consistent measurements show numerous departures from previously published results. We show that the compound adopts a k = [010 ] antiferromagnetic structure with the moment directions mostly along the a axis, and that the paramagnetic susceptibility is isotropic. The critical behavior was also investigated through the temperature dependence of the magnetic Bragg peaks below the Néel temperature.

  11. Femtosecond optomagnetism in dielectric antiferromagnets

    Science.gov (United States)

    Bossini, D.; Rasing, Th

    2017-02-01

    Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.

  12. Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, I.A.

    2006-07-01

    studied how the interplay of precession and damping affects various thermodynamic and transport quantities. We found that the susceptibility {chi}={delta}M/{delta}B is the thermodynamic quantity which shows the most significant change upon approaching the quantum critical point and which gives experimental access to the (dangerously irrelevant) spin-spin interactions. Finally, we studied the quantum critical behaviour of two-dimensional antiferromagnetic metals. Going beyond an order parameter theory, we included the electronic quasiparticles as well as the fluctuating magnetization in a functional Renormalization Group calculation. Preliminary results indicate a divergence in the fRG-equations already at a finite distance from the quantum critical point. this is incompatible with the Hertz-Millis picture. (orig.)

  13. Spin Superfluidity in Biaxial Antiferromagnetic Insulators

    Science.gov (United States)

    Qaiumzadeh, Alireza; Skarsvâg, Hans; Holmqvist, Cecilia; Brataas, Arne

    2017-03-01

    Antiferromagnets may exhibit spin superfluidity since the dipole interaction is weak. We seek to establish that this phenomenon occurs in insulators such as NiO, which is a good spin conductor according to previous studies. We investigate nonlocal spin transport in a planar antiferromagnetic insulator with a weak uniaxial anisotropy. The anisotropy hinders spin superfluidity by creating a substantial threshold that the current must overcome. Nevertheless, we show that applying a high magnetic field removes this obstacle near the spin-flop transition of the antiferromagnet. Importantly, the spin superfluidity can then persist across many micrometers, even in dirty samples.

  14. Heisenberg antiferromagnets with exchange and cubic anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Bannasch, G [MPI fuer Physik komplexer Systeme, 01187 Dresden (Germany); Selke, W, E-mail: selke@physik.rwth-aachen.d [Institut fuer Theoretische Physik, RWTH Aachen University and JARA-SIM, 52056 Aachen (Germany)

    2010-01-01

    We study classical Heisenberg antiferromagnets with uniaxial exchange anisotropy and a cubic anisotropy term on simple cubic lattices in an external magnetic field using ground state considerations and extensive Monte Carlo simulations. In addition to the antiferromagnetic phase field-induced spin-flop and non-collinear, biconical phases may occur. Phase diagrams and critical as well as multicritical phenomena are discussed. Results are compared to previous findings.

  15. Neutron scattering studies of three one-dimensional antiferromagnets

    CERN Document Server

    Kenzelmann, M

    2001-01-01

    observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs sub 2 CoCl sub 4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. Low-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNi...

  16. Electric-field-induced antiferromagnetic resonance in antiferromagnetic insulators with spin-orbit coupling

    Directory of Open Access Journals (Sweden)

    Akihiko Sekine

    2017-05-01

    Full Text Available We study theoretically spin dynamics in three-dimensional antiferromagnetic insulators with spin-orbit coupling. We focus on the antiferromagnetic insulators whose low-energy effective model possesses a topological term called the θ term. By solving the Landau-Lifshitz-Gilbert equation in the presence of the θ term, we show that the antiferromagnetic resonance can be realized by ac electric fields along with static magnetic fields. The antiferromagnetic resonance can be detected via the spin pumping from the Néel field and net magnetization. We calculate both contributions to the pumped spin current, and find that the magnitude of the ac electric field to cause the resonance state is very small (∼ 1 V/m. This indicates that spin currents can be generated efficiently. The mechanism of the antiferromagnetic resonance in this study is understood as the inverse process of the dynamical chiral magnetic effect.

  17. Antiferromagnetic Excitations and Van Hove Singularities in YBa$_2$Cu$_3$O$_{6+x}$

    OpenAIRE

    Blumberg, G.; Stojkovic, Branko P.; Klein, M. V.

    1995-01-01

    We show that in quasi-two-dimensional $d$-wave superconductors Van Hove singularities close to the Fermi surface lead to novel magnetic quasi-particle excitations. We calculate the temperature and doping dependence of dynamical magnetic susceptibility for YBCO and show that the proposed excitations are in agreement with inelastic neutron scattering experiments. In addition, the values of the gap parameter and in-plane antiferromagnetic coupling are much smaller than usually believed.

  18. High temperature series expansions for the susceptibility of Ising model on the Kagome lattice with nearest neighber interactions

    Directory of Open Access Journals (Sweden)

    Z Jalali mola

    2011-12-01

    Full Text Available  The Ising model is one of the simplest models describing the interacting particles. In this work, we calculate the high temperature series expansions of zero field susceptibility of ising model with ferromagnetic, antiferromagnetic and one antiferromagnetic interactions on two dimensional kagome lattice. Using the Pade´ approximation, we calculate the susceptibility of critical exponent of ferromagnetic ising model γ ≈ 1.75, which is consistent with universality hypothesis. However, antiferromagnetic and one antiferromagnetic interaction ising model doesn’t show any transition at finite temperature because of the effect of magnetic frustration.

  19. Antiferromagnetic Spin Wave Field-Effect Transistor

    Science.gov (United States)

    Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di

    2016-01-01

    In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale. PMID:27048928

  20. Itinerant Antiferromagnetism in RuO2

    Science.gov (United States)

    Berlijn, T.; Snijders, P. C.; Delaire, O.; Zhou, H.-D.; Maier, T. A.; Cao, H.-B.; Chi, S.-X.; Matsuda, M.; Wang, Y.; Koehler, M. R.; Kent, P. R. C.; Weitering, H. H.

    2017-02-01

    Bulk rutile RuO2 has long been considered a Pauli paramagnet. Here we report that RuO2 exhibits a hitherto undetected lattice distortion below approximately 900 K. The distortion is accompanied by antiferromagnetic order up to at least 300 K with a small room temperature magnetic moment of approximately 0.05 μB as evidenced by polarized neutron diffraction. Density functional theory plus U (DFT +U ) calculations indicate that antiferromagnetism is favored even for small values of the Hubbard U of the order of 1 eV. The antiferromagnetism may be traced to a Fermi surface instability, lifting the band degeneracy imposed by the rutile crystal field. The combination of high Néel temperature and small itinerant moments make RuO2 unique among ruthenate compounds and among oxide materials in general.

  1. Magnetic correlations in the intermetallic antiferromagnet Nd3Co4Sn13

    Science.gov (United States)

    Wang, C. W.; Lin, J. W.; Lue, C. S.; Liu, H. F.; Kuo, C. N.; Mole, R. A.; Gardner, J. S.

    2017-11-01

    Specific heat, magnetic susceptibility, and neutron scattering have been used to investigate the nature of the spin system in the antiferromagnet Nd3Co4Sn13. At room temperature Nd3Co4Sn13 has a cubic, Pm-3n structure similar to Yb3Rh4Sn13. Antiferromagnetic interactions between, Nd3+ ions dominate the magnetic character of this sample and at 2.4 K the Nd spins enter a long range order state with a magnetic propagation vector q  =  (0 0 0) with an ordered moment of 1.78(2) µ B at 1.5 K. The magnetic Bragg intensity grows very slowly below 1 K, reaching ~2.4 µ B at 350 mK. The average magnetic Nd3+ configuration corresponds to the 3D irreducible representation Γ7. This magnetic structure can be viewed as three sublattices of antiferromagnetic spin chains coupled with each other in the 120°-configuration. A well-defined magnetic excitation was measured around the 1 1 1 zone centre and the resulting dispersion curve is appropriate for an antiferromagnet with a gap of 0.20(1) meV.

  2. Quantum Spin Liquid Emerging from Antiferromagnetic Order by Introducing Disorder.

    Science.gov (United States)

    Furukawa, T; Miyagawa, K; Itou, T; Ito, M; Taniguchi, H; Saito, M; Iguchi, S; Sasaki, T; Kanoda, K

    2015-08-14

    Quantum spin liquids, which are spin versions of quantum matter, have been sought after in systems with geometrical frustration. We show that disorder drives a classical magnet into a quantum spin liquid through conducting NMR experiments on an organic Mott insulator, κ-(ET)_{2}Cu[N(CN)_{2}]Cl. Antiferromagnetic ordering in the pristine crystal, when irradiated by x rays, disappears. Spin freezing, spin gap, and critical slowing down are not observed, but gapless spin excitations emerge, suggesting a novel role of disorder that brings forth a quantum spin liquid from a classical ordered state.

  3. Antiferromagnets Structure in Adsorbed O2 Monolayers

    DEFF Research Database (Denmark)

    Nielsen, Mourits; McTague, J. P.

    1977-01-01

    Neutron diffraction from monolayers of O2 adsorbed on graphite shows structural arrangements similar to the dense planes of bulk O2. At monolayer completion and above, a magnetic superlattice reflection shows well-developed antiferromagnetic order for T ⩽ 10 K. The submonolayer phase also shows s...

  4. Antiferromagnetism in chromium alloy single crystals

    DEFF Research Database (Denmark)

    Bjerrum Møller, Hans; Trego, A.L.; Mackintosh, A.R.

    1965-01-01

    The antiferromagnetism of single crystals of dilute alloys of V, Mn and Re in Cr has been studied at 95°K and 300°K by neutron diffraction. The addition of V causes the diffraction peaks to decrease in intensity and move away from (100), while Mn and Re cause them to increase and approach (100) s...

  5. The electronic structure of antiferromagnetic chromium

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt

    1981-01-01

    The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...

  6. Antiferromagnetic noise correlations in optical lattices

    DEFF Research Database (Denmark)

    Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.

    2009-01-01

    We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we s...

  7. Thermoinduced magnetization in nanoparticles of antiferromagnetic materials

    DEFF Research Database (Denmark)

    Mørup, Steen; Frandsen, Cathrine

    2004-01-01

    We show that there is a thermoinduced contribution to the magnetic moment of nanoparticles of antiferromagnetic materials. It arises from thermal excitations of the uniform spin-precession mode, and it has the unusual property that its magnitude increases with increasing temperature. This has the...

  8. Canted Antiferromagnetism on Rectangular Layers of Fe2+ in Polymorphic CaFeSeO.

    Science.gov (United States)

    Lai, Kwing To; Komarek, Alexander Christoph; Fernández-Díaz, Maria Teresa; Chang, Pi-Shan; Huh, Sungjoon; Rosner, Helge; Kuo, Chang-Yang; Hu, Zhiwei; Pi, Tun-Wen; Adler, Peter; Ksenofontov, Vadim; Tjeng, Liu Hao; Valldor, Martin

    2017-04-17

    From stoichiometric amounts of CaO, Fe, and Se, pure powders and single crystals of quaternary [Formula: see text] can be obtained by solid-state reaction and self-flux growth, respectively. The as-synthesized compound exhibits a polymorphic crystal structure, where the two modifications have different stacking sequences of [Formula: see text] layers. The two polymorphs have similar unit cells but different crystal symmetries (Cmc21 and Pnma), of which the former is non-centrosymmetric. Fe is divalent (d6) and high-spin, as proven by X-ray spectroscopy, Mössbauer spectroscopy, and powder neutron diffraction data. The latter two, in combination with magnetic susceptibility and specific heat data, reveal a long-range antiferromagnetic spin order (TN = 160 K) with a minor spin canting. CaFeSeO is an electronic insulator, as confirmed by resistivity measurements and density functional theory calculations. The latter also suggest a relatively small energy difference between the two polymorphs, explaining their intimate intergrowth.

  9. Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

    Directory of Open Access Journals (Sweden)

    Joseph Sklenar

    2016-05-01

    Full Text Available We investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. We also suggest that metallic antiferromagnets may be good candidates for the investigation of various unidirectional effects related to novel spin-orbitronics phenomena.

  10. Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

    Energy Technology Data Exchange (ETDEWEB)

    Sklenar, Joseph [Materials Science Division, Argonne National Laboratory, Lemont IL 60439 (United States); Department of Physics and Astronomy, Northwestern University, Evanston IL 60208 (United States); Zhang, Wei, E-mail: zwei@anl.gov; Jungfleisch, Matthias B.; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel [Materials Science Division, Argonne National Laboratory, Lemont IL 60439 (United States); Saglam, Hilal [Materials Science Division, Argonne National Laboratory, Lemont IL 60439 (United States); Department of Physics, Illinois Institute of Technology, Chicago IL 60616 (United States); Ketterson, John B. [Department of Physics and Astronomy, Northwestern University, Evanston IL 60208 (United States)

    2016-05-15

    We investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. We also suggest that metallic antiferromagnets may be good candidates for the investigation of various unidirectional effects related to novel spin-orbitronics phenomena.

  11. Modeling anisotropic magnetoresistance in layered antiferromagnets

    Science.gov (United States)

    Santos, D. L. R.; Pinheiro, F. A.; Velev, J.; Chshiev, M.; Castro, J. d.'Albuquerque e.; Lacroix, C.

    2017-06-01

    We have investigated the electronic transport and the anisotropic magnetoresistance in systems consisting of pairs of antiferromagnetically aligned layers separated by a non-magnetic layer, across which an antiferromagnetic coupling between the double layers is established. Calculations have been performed within the framework of the tight-binding model, taking into account the exchange coupling within the ferromagnetic layers and the Rashba spin-orbit interaction. Conductivities have been evaluated in the ballistic regime, based on Kubo formula. We have systematically studied the dependence of the conductivity and of the anisotropic magnetoresistance on several material and structural parameters, such as the orientation of the magnetic moments relative to the crystalline axis, band filling, out-of-plane hopping and spin-orbit parameter.

  12. Dynamic rotor mode in antiferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Lefmann, Kim; Jacobsen, H.; Garde, J.

    2015-01-01

    We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K....... However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all...

  13. Spin Transport in Ferromagnetic and Antiferromagnetic Textures

    KAUST Repository

    Akosa, Collins A.

    2016-12-07

    In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.

  14. Robust spin transfer torque in antiferromagnetic tunnel junctions

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed

    2017-04-18

    We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque enabling electrical manipulation of the Néel antiferromagnetic order parameter is out of plane, ∼n×p, while the torque competing with the antiferromagnetic exchange is in plane, ∼n×(p×n). Here, p and n are the Néel order parameter direction of the reference and free layers, respectively. Their bias dependence shows behavior similar to that in ferromagnetic tunnel junctions, the in-plane torque being mostly linear in bias, while the out-of-plane torque is quadratic. Most importantly, we find that the spin transfer torque in antiferromagnetic tunnel junctions is much more robust against disorder than that in antiferromagnetic metallic spin valves due to the tunneling nature of spin transport.

  15. Biconical structures in two-dimensional anisotropic Heisenberg antiferromagnets

    OpenAIRE

    Holtschneider, M.; Selke, W.

    2007-01-01

    Square lattice Heisenberg and XY antiferromagnets with uniaxial anisotropy in a field along the easy axis are studied. Based on ground state considerations and Monte Carlo simulations, the role of biconical structures in the transition region between the antiferromagnetic and spin--flop phases is analyzed. In particular, adding a single--ion anisotropy to the XXZ antiferromagnet, one observes, depending on the sign of that anisotropy, either an intervening biconical phase or a direct transiti...

  16. Magnetic Properties of Nanoparticles of Antiferromagnetic Materials

    DEFF Research Database (Denmark)

    Mørup, Steen; Frandsen, Cathrine; Bødker, Franz

    2003-01-01

    The magnetic properties of antiferromagnetic nanoparticles have been studied by Mossbauer spectroscopy and neutron scattering. Temperature series of Mossbauer spectra of non-interacting, superparamagnetic hematite nanoparticles were fitted by use of the Blume-Tjon relaxation model. It has been...... of the parameters obtained from Mossbauer spectroscopy and neutron scattering. In samples of interacting hematite nanoparticles, the relaxation was significantly suppressed. The Mossbauer data for these samples are in accordance with a mean field model for an ordered state of strongly interacting particles. Mixing...... nanoparticles of hematite with CoO nanoparticles resulted in suppression of the superparamagnetic relaxation, whereas NiO nanoparticles had the opposite effect....

  17. Classical and quantum anisotropic Heisenberg antiferromagnets

    Directory of Open Access Journals (Sweden)

    W. Selke

    2009-01-01

    Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.

  18. Switching of antiferromagnetic chains with magnetic pulses

    Science.gov (United States)

    Tao, Kun; Polyakov, Oleg P.; Stepanyuk, Valeri S.

    2016-04-01

    Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012), 10.1126/science.1214131]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.

  19. High magnetic field magnetization of a new triangular lattice antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, H. D. [Univ. of Tennessee, Knoxville, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab); Stritzinger, Laurel Elaine Winter [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Harrison, Neil [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-23

    In CsV(MoO4)2, the magnetic V3+ ions with octahedral oxygen-coordination form a geometrically frustrated triangular lattice. So fare, there is no magnetic properties reported on it. Recently, we successfully grew single crystals of CsV(MoO4)2 by using flux method. The susceptibility shows a sharp drop around 24 K, representing a long range magnetic ordering. To understand the physical properties of this new triangular lattice antiferromagnet (TLAF), we pursued high field magnetization measurements to answer two questions: (i) what is the saturation field, which will be very useful to calculate the exchange interaction of the system? (ii) Will it exhibit spin state transition, such as the up up down phase with 1/3-saturation moment as other TLAFs? Recently, we performed VSM measurements in Cell 8, Tallahassee, NHMFL, the results show that the magnetization reaches 0.38 MuB at 34 T, which is just 19% of the full moment of 2 MuB for V3+ (3d2) ions. Apparently we need higher field to reach 1/3 value or full moment.

  20. The antiferromagnetic Ising model for a bilayer Bethe lattice

    Energy Technology Data Exchange (ETDEWEB)

    Albayrak, Erhan [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)], E-mail: albayrak@erciyes.edu.tr; Yigit, Ali; Akkaya, Seyma [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)

    2008-09-15

    The totally antiferromagnetic Ising model is analyzed on a bilayer Bethe lattice in detail by studying the order-parameters, response functions, i.e. susceptibility and specific heat, and free energy by using the recursion relations in a pairwise approach. The ground state phase diagrams of the model are also obtained on the (J{sub 2}/|J{sub 1}|,J{sub 3}/q|J{sub 1}|) plane for given values of H/q|J{sub 1}| and on the (H/q|J{sub 1}|,J{sub 3}/q|J{sub 1}|) plane for given J{sub 2}/|J{sub 1}|. As a result, we have obtained the temperature-dependent phase diagrams for various values of the coordination number q on the (J{sub 3}/|J{sub 1}|,kT/|J{sub 1}|) and (H/|J{sub 1}|,kT/|J{sub 1}|) planes for given values of the rest of the system parameters.

  1. Antiferromagnetic Dirac semimetals in two dimensions

    Science.gov (United States)

    Wang, Jing

    2017-03-01

    The search for symmetry-protected two-dimensional (2D) Dirac semimetals analogous to graphene is important both for fundamental and practical interest. The 2D Dirac cones are protected by crystalline symmetries and magnetic ordering may destroy their robustness. Here we propose a general framework to classify stable 2D Dirac semimetals in spin-orbit coupled systems having the combined time-reversal and inversion symmetries, and show the existence of the stable Dirac points in 2D antiferromagnetic semimetals. Compared to 3D Dirac semimetals which fall into two distinct classes, Dirac semimetals in 2D with combined time-reversal and inversion symmetries belong to a single class which is closely related to the nonsymmorphic space-group symmetries. We further provide a concrete model in antiferromagnetic semimetals which supports symmetry-protected 2D Dirac points. The symmetry breaking in such systems leads to 2D chiral topological states such as quantum anomalous Hall insulator and chiral topological superconductor phases.

  2. Topological gapless phases in nonsymmorphic antiferromagnets

    Science.gov (United States)

    Brzezicki, Wojciech; Cuoco, Mario

    2017-04-01

    We investigate the nature of the electronic states in a variety of nonsymmorphic collinear antiferromagnets with glide reflection symmetry, a combination of mirror and half-lattice translation. In particular, the study refers to a class of systems with two-band itinerant electrons that are spin-orbit coupled and interacting with a magnetic background having a zigzag pattern. We describe the symmetry properties of the model system by focusing on the role of nonsymmorphic transformations arising from the antiferromagnetic structure of the spin ordering. Gapless phases with Dirac points having different types of symmetry-protection as well as electronic structures with triple and quadruple band-crossing points are obtained. A glide semimetal is shown to be converted into a gapless phase with Dirac points protected by inversion and time-inversion symmetry combination. Interestingly, we find a relation between the states in the glide sectors that provides a general mechanism to get multiple band touching points. The split of the multiple Fermi points drives the transition from a point node to a line node semimetal or to a metal with nontrivial winding around the Fermi pockets and an electronic structure that is tied to the presence of glide symmetric Dirac points. Besides a new perspective of ordered states in complex materials, our findings indicate relevant paths to topological gapless phases and edge states in a wide class of magnetic systems.

  3. Magnetic susceptibility of oxygen adsorbed on the surface of spherical and fibrous activated carbon.

    Directory of Open Access Journals (Sweden)

    Kiyoshi Kawamura

    2009-02-01

    Full Text Available The magnetic susceptibilities of oxygen adsorbed on the surface of bead-shaped activated carbon and activated carbon fibers were evaluated as a function of temperature between 4.2 K and 300 K, and found to exhibit a sharp peak at around 50 K. This implies that the adsorbed oxygen molecules form an antiferromagnetic state. The relation between the susceptibility and the adsorbed mass suggest that the thickness of the adsorbed oxygen is thin enough to consider a two-dimensional structure for bead–shaped activated carbon and carbon fibers across the fiber axis but thick enough to regard it as three-dimensional along the fiber axis. The result is discussed with reference to the study on one-dimensional oxygen array.

  4. Superconductivity, Antiferromagnetism, and Kinetic Correlation in Strongly Correlated Electron Systems

    Directory of Open Access Journals (Sweden)

    Takashi Yanagisawa

    2015-01-01

    Full Text Available We investigate the ground state of two-dimensional Hubbard model on the basis of the variational Monte Carlo method. We use wave functions that include kinetic correlation and doublon-holon correlation beyond the Gutzwiller ansatz. It is still not clear whether the Hubbard model accounts for high-temperature superconductivity. The antiferromagnetic correlation plays a key role in the study of pairing mechanism because the superconductive phase exists usually close to the antiferromagnetic phase. We investigate the stability of the antiferromagnetic state when holes are doped as a function of the Coulomb repulsion U. We show that the antiferromagnetic correlation is suppressed as U is increased exceeding the bandwidth. High-temperature superconductivity is possible in this region with enhanced antiferromagnetic spin fluctuation and pairing interaction.

  5. Probing the evolution of antiferromagnetism in multiferroics

    Energy Technology Data Exchange (ETDEWEB)

    Holcomb, M.; Martin, L.; Scholl, A.; He, Q.; Yu, P.; Yang, C.-H.; Yang, S.; Glans, P.-A.; Valvidares, M.; Huijben, M.; Kortright, J.; Guo,, J.; Chu, Y.-H.; Ramesh, R.

    2010-06-09

    This study delineates the evolution of magnetic order in epitaxial films of the room-temperature multiferroic BiFeO3 system. Using angle- and temperature-dependent dichroic measurements and spectromicroscopy, we have observed that the antiferromagnetic order in the model multiferroic BiFeO3 evolves systematically as a function of thickness and strain. Lattice-mismatch-induced strain is found to break the easy-plane magnetic symmetry of the bulk and leads to an easy axis of magnetization which can be controlled through strain. Understanding the evolution of magnetic structure and how to manipulate the magnetism in this model multiferroic has significant implications for utilization of such magnetoelectric materials in future applications.

  6. Computational design of a robust two-dimensional antiferromagnetic semiconductor

    Science.gov (United States)

    Chabungbam, Satyananda; Sen, Prasenjit

    2017-07-01

    Using density functional theory calculations, we establish the hitherto unknown compound CrCTe3 to be a stable antiferromagnetic semiconductor in the R 3 ¯ crystal structure with an indirect fundamental gap. Successive layers in the bulk compound are weakly bound by van der Waals forces so that individual layers can be easily exfoliated. A monolayer of CrCTe3 is also an antiferromagnetic semiconductor. The monolayer is structurally stable over a large range of compressive and tensile strains, and the antiferromagnetic state is robust over this strain range. Band gap of the monolayer can be tuned by as much as 50% by applying strain in this range.

  7. Three-band Hubbard model for Na2IrO3 : Topological insulator, zigzag antiferromagnet, and Kitaev-Heisenberg material

    Science.gov (United States)

    Laubach, Manuel; Reuther, Johannes; Thomale, Ronny; Rachel, Stephan

    2017-09-01

    Na2IrO3 was one of the first materials proposed to feature the Kane-Mele-type topological insulator phase. Contemporaneously it was claimed that the very same material is in a Mott insulating phase which is described by the Kitaev-Heisenberg (KH) model. First experiments indeed revealed Mott insulating behavior in conjunction with antiferromagnetic long-range order. Further refined experiments established antiferromagnetic order of zigzag type which is not captured by the KH model. Since then several extensions and modifications of the KH model were proposed in order to describe the experimental findings. Here we suggest that adding charge fluctuations to the KH model represents an alternative explanation of zigzag antiferromagnetism. Moreover, a phenomenological three-band Hubbard model unifies all the pieces of the puzzle: topological insulator physics for weak and KH model for strong electron-electron interactions as well as a zigzag antiferromagnet at intermediate interaction strength.

  8. (H,Ti)-diagram of magnetic transformations induced by a pulsed magnetic field in antiferromagnetic LiCoPO4

    Science.gov (United States)

    Khrustalyov, V. M.; Savytsky, V. N.; Kharchenko, M. F.

    2017-11-01

    A study of the differential magnetic susceptibility and electric polarization of an antiferromagnetic LiCoPO4 crystal in a pulsed magnetic field with an intensity of up to 290 kOe, directed along the antiferromagnetism vector of the spin-ordering main mode (Hǁb), at initial sample temperatures between 1.6 and 20.8 K. An adiabatic (H, Ti)-diagram of magnetic phase transitions is constructed. In addition to the three transitions that were discovered earlier at helium temperatures, higher temperatures revealed singularities that indicate the existence of a first-order phase transition line in the high-field phase II, which ends at a critical point. The coordinates of the critical point at which the lines of the phase transitions bordering the region of existence of high-field phase III converge with the line of the phase transitions from phase II to the saturated paramagnetic phase, are also determined.

  9. Skyrmion defects and competing singlet orders in a half-filled antiferromagnetic Kondo-Heisenberg model on the honeycomb lattice

    Science.gov (United States)

    Liu, Chia-Chuan; Goswami, Pallab; Si, Qimiao

    2017-09-01

    Due to the interaction between the topological defects of an order parameter and underlying fermions, the defects can possess induced fermion numbers, leading to several exotic phenomena of fundamental importance to both condensed matter and high-energy physics. One of the intriguing outcomes of induced fermion numbers is the presence of fluctuating competing orders inside the core of a topological defect. In this regard, the interaction between fermions and skyrmion excitations of an antiferromagnetic phase can have important consequences for understanding the global phase diagrams of many condensed matter systems where antiferromagnetism and several singlet orders compete. We critically investigate the relation between fluctuating competing orders and skyrmion excitations of the antiferromagnetic insulating phase of a half-filled Kondo-Heisenberg model on a honeycomb lattice. By combining analytical and numerical methods, we obtain the exact eigenstates of underlying Dirac fermions in the presence of a single skyrmion configuration, which are used for computing the induced chiral charge. Additionally, by employing this nonperturbative eigenbasis, we calculate the susceptibilities of different translational symmetry breaking charges, bond and current density wave orders, and translational symmetry preserving Kondo singlet formations. Based on the computed susceptibilities, we establish spin Peierls and Kondo singlets as dominant competing orders of antiferromagnetism. We show favorable agreement between our findings and field theoretic predictions based on the perturbative gradient expansion scheme, which crucially relies on the adiabatic principle and plane-wave eigenstates for Dirac fermions. The methodology developed here can be applied to many other correlated systems supporting competition between spin-triplet and spin-singlet orders in both lower and higher spatial dimensions.

  10. A Spin-Canted Antiferromagnetic Ground State in CeRu2Al10

    Science.gov (United States)

    Dean, Philip; Muro, Yuji; Takabatake, Toshiro; Hatton, Peter D.

    2018-01-01

    Resonant polarised soft x-ray scattering at the cerium M-edge has been used to refine the magnetic structure of CeRu2Al10. A strong resonant feature at the cerium MIV-edge was observed at the disallowed (0,1,0) Bragg position, consistent with previous neutron diffraction refinement of the moment pointing along the c-axis. The magnetic peak was found to have a temperature dependence expected for the paramagnetic-antiferromagnetic transition, disappearing above around 30 K. The polarisation dependence of the scattered x-rays conclusively shows that the low-temperature antiferromagnetic structure is non-collinear in nature. Fitting the polarisation dependence of the obtained Stokes parameters was undertaken with models for canting along either the a-axis or the b-axis. The experimental data agrees better with the model involving canting towards the a-axis. However, this is inconsistent with the Cmcm space group, suggestive of a symmetry lowering to either Pmnm or Cm2m. The resulting model is then achieved with a 9.6° ± 1.1 canting of the moments towards the a-axis. No resonance features were observed at the ruthenium L-edges. This suggests that the ruthenium atoms play no part in the antiferromagnetic ordering.

  11. Kinetically Inhibited Order in a Diamond-Lattice Antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    MacDougall, Gregory J [ORNL; Gout, Delphine J [ORNL; Zarestky, Jerel L [ORNL; Ehlers, Georg [ORNL; Podlesnyak, Andrey A [ORNL; McGuire, Michael A [ORNL; Mandrus, David [ORNL; Nagler, Stephen E [ORNL

    2011-01-01

    Frustrated magnetic systems exhibit highly degenerate ground states and strong fluctuations, often leading to new physics. An intriguing example of current interest is the antiferromagnet on a diamond lattice, realized physically in the A-site spinel materials. This is a prototypical system in three dimensions where frustration arises from competing interactions rather than purely geometric constraints, and theory suggests the possibility of novel order at low temperature. Here we present a comprehensive single crystal neutron scattering study CoAl2O4, a highly frustrated A-site spinel. We observe strong diffuse scattering that peaks at wavevectors associated with Neel ordering. Below the temperature T*=6.5K, there is a dramatic change in elastic scattering lineshape accompanied by the emergence of well-defined spin-wave excitations. T* had previously been associated with the onset of glassy behavior. Our new results suggest instead that in fact T* signifies a first-order phase transition, but with true long-range order inhibited by the kinetic freezing of domain walls. This scenario might be expected to occur widely in frustrated systems containing first-order phase transitions and is a natural explanation for existing reports of anomalous glassy behavior in other materials.

  12. Antiferromagnetic Skyrmion: Stability, Creation and Manipulation.

    Science.gov (United States)

    Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko

    2016-04-21

    Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.

  13. Landau model for the multiferroic delafossite antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, J.L, E-mail: jlr@fisica.uminho.pt [Centro de Física da Universidade do Minho, 4710-057 Braga (Portugal); Perez-Mato, J.M [Dpto. de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao (Spain); Vieira, L.G [Centro de Física da Universidade do Minho, 4710-057 Braga (Portugal)

    2016-10-15

    A symmetry based framework is used to describe the complex phase diagrams observed in the multiferroic delafossite compounds. A free energy Landau functional is derived from the analysis of the transformation properties of the most general incommensurate magnetic spin order parameter. A principle of maximal symmetry is invoked and the stability of each of the different higher symmetry phases considered. The competition between different potential ground states is analysed within the scope of a simplified model, which emphasizes the role of the symmetry allowed phase dependent biquadratic couplings. The cross-over between the different competing states is also discussed. The results show that the diverse set of phase diagrams that are experimentally observed in this class of triangular lattice antiferromagnets and, in particular, the stabilization of magnetically induced ferroelectric states, can be well interpreted and described within this integrated phenomenological approximation. - Highlights: • Symmetry considerations are used to analyze the phase diagrams of the compounds. • The competition between possible ground states is discussed. • The field induced transitions between competing states are described.

  14. Robust ferromagnetism carried by antiferromagnetic domain walls

    Science.gov (United States)

    Hirose, Hishiro T.; Yamaura, Jun-Ichi; Hiroi, Zenji

    2017-02-01

    Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

  15. Spin-Mechanical Inertia in Antiferromagnet

    Science.gov (United States)

    Cheng, Ran; Wu, Xiaochuan; Xiao, Di

    Interplay between spin dynamics and mechanical motions is responsible for numerous striking phenomena, which has shaped a rapidly expanding field known as spin-mechanics. The guiding principle of this field has been the conservation of angular momentum that involves both quantum spins and classical mechanical rotations. However, in an antiferromagnet, the macroscopic magnetization vanishes while the order parameter (Néel order) does not carry an angular momentum. It is therefore not clear whether the order parameter dynamics has any mechanical consequence as its ferromagnetic counterparts. Here we demonstrate that the Néel order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperature when magnon excitations are considered. Such a spin-mechanical inertia can produce measurable consequences at nanometer scales. Our discovery establishes spin-mechanical inertia as an essential ingredient to properly describe spin-mechanical effects in AFs, which supplements the known governing physics from angular momentum conservation. This work was supported by the DOE, Basic Energy Sciences, Grant No. DE-SC0012509. D.X. also acknowledges support from a Research Corporation for Science Advancement Cottrell Scholar Award.

  16. Spin-frustrated antiferromagnets based on BEDT-TTF and manganese dicyanamide complexes

    Science.gov (United States)

    Morgunov, R. B.; Kurganova, E. V.; Tanimoto, Y.; Markosyan, A. S.; Kazakova, A. V.; Kushch, N. D.; Yagubskiĭ, É. B.; Dubrovskiĭ, A. D.; Shilov, G. V.

    2007-05-01

    The magnetic properties of new radical cation salts ( BEDT-TTF)2[CuMn( dca)4] ( I) and ( BEDT-TTF)2[Mn( dca)3] ( II) [where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene and dca = N(CN2)] are investigated using superconducting quantum interference device (SQUID) magnetometry and electron paramagnetic resonance (EPR) spectroscopy. It is established that, at temperatures below 25 K, both salts are characterized by antiferromagnetic deviations from the paramagnetic behavior. The Weiss constants for compounds I and II are determined to be -5 and -10 K, respectively. The corresponding correlations in the structure of compound I are short-range correlations and do not lead to a change in the effective spin equal to 5/2. It is found that the widths of the EPR lines attributed to the BEDT-TTF conducting sublattice correlate with the widths of the EPR lines associated with the magnetic sublattice of the Mn( dca){3/-} counterion in the structure of salt II. This correlation suggests that the antiferromagnetic ordering in the magnetic sublattice of compound II affects the spin-lattice relaxation in the BEDT-TTF sublattice. The dependence of the magnetic moment on the magnetic field for compound II at a temperature of 2 K is typical of weakly frustrated uniaxial antiferromagnets and exhibits a kink in a magnetic field of 20 kOe, which corresponds to spin-flop transitions.

  17. Antiferromagnetic Resonance and Terahertz Continuum in α -RuCl3

    Science.gov (United States)

    Little, A.; Wu, Liang; Lampen-Kelley, P.; Banerjee, A.; Patankar, S.; Rees, D.; Bridges, C. A.; Yan, J.-Q.; Mandrus, D.; Nagler, S. E.; Orenstein, J.

    2017-12-01

    We report measurements of optical absorption in the zigzag antiferromagnet α -RuCl3 as a function of temperature T , magnetic field B , and photon energy ℏω in the range ˜0.3 -8.3 meV, using time-domain terahertz spectroscopy. Polarized measurements show that threefold rotational symmetry is broken in the honeycomb plane from 2 to 300 K. We find a sharp absorption peak at 2.56 meV upon cooling below the Néel temperature of 7 K at B =0 that we identify as the magnetic-dipole excitation of a zero-wave-vector magnon, or antiferromagnetic resonance (AFMR). With the application of B , the AFMR broadens and shifts to a lower frequency as long-range magnetic order is lost in a manner consistent with transitioning to a spin-disordered phase. From a direct, internally calibrated measurement of the AFMR spectral weight, we place an upper bound on the contribution to the dc susceptibility from a magnetic excitation continuum.

  18. Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

    Science.gov (United States)

    Galceran, R.; Fina, I.; Cisneros-Fernández, J.; Bozzo, B.; Frontera, C.; López-Mir, L.; Deniz, H.; Park, K.-W.; Park, B.-G.; Balcells, Ll.; Martí, X.; Jungwirth, T.; Martínez, B.

    2016-10-01

    Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature.

  19. Er2Ti2O7: Evidence of quantum order by disorder in a frustrated antiferromagnet

    DEFF Research Database (Denmark)

    Champion, J.D.M.; Harris, M.J.; Holdsworth, P.C.W.

    2003-01-01

    Er(2)Ti(2)O(7) has been suggested to be a realization of the frustrated XY pyrochlore lattice antiferromagnet, for which theory predicts fluctuation-induced symmetry breaking in a highly degenerate ground state manifold. We present a theoretical analysis of the classical model compared...... to neutron scattering experiments on the real material, both below and above T(N)=1.173(2) K. The model correctly predicts the ordered magnetic structure, suggesting that the real system has order stabilized by zero-point quantum fluctuations that can be modeled by classical spin wave theory. However...

  20. High-resolution Monte Carlo study of the multicritical point in the three-dimensional XXZ Heisenberg antiferromagnet

    Science.gov (United States)

    Hu, Siyan; Tsai, Shan-Ho; Landau, D. P.

    2014-03-01

    We use Monte Carlo simulations to study the XXZ Heisenberg antiferromagnet in a field in order to clearly determine the nature of the multicritical point. We use a hybrid sampling method with Metropolis and Wolff-cluster algorithms, along with histogram reweighting techniques. Staggered magnetization susceptibilities, Binder cumulants, and finite-size scaling are considered in an effort to detect a possible biconical phase. An analysis of the probability distribution of the magnetization allowed us to conclude that the multicritical point is bicritical and it is in the three-dimensional Heisenberg universality class.

  1. Orphan Spins in the S =5/2 Antiferromagnet CaFe2O4

    Science.gov (United States)

    Stock, C.; Rodriguez, E. E.; Lee, N.; Demmel, F.; Fouquet, P.; Laver, M.; Niedermayer, Ch.; Su, Y.; Nemkovski, K.; Green, M. A.; Rodriguez-Rivera, J. A.; Kim, J. W.; Zhang, L.; Cheong, S.-W.

    2017-12-01

    CaFe2O4 is an anisotropic S =5/2 antiferromagnet with two competing A (↑↑↓↓) and B (↑↓↑↓) magnetic order parameters separated by static antiphase boundaries at low temperatures. Neutron diffraction and bulk susceptibility measurements, show that the spins near these boundaries are weakly correlated and a carry an uncompensated ferromagnetic moment that can be tuned with a magnetic field. Spectroscopic measurements find these spins are bound with excitation energies less than the bulk magnetic spin waves and resemble the spectra from isolated spin clusters. Localized bound orphaned spins separate the two competing magnetic order parameters in CaFe2 O4 .

  2. Orphan Spins in the S=5/2 Antiferromagnet CaFe_{2}O_{4}.

    Science.gov (United States)

    Stock, C; Rodriguez, E E; Lee, N; Demmel, F; Fouquet, P; Laver, M; Niedermayer, Ch; Su, Y; Nemkovski, K; Green, M A; Rodriguez-Rivera, J A; Kim, J W; Zhang, L; Cheong, S-W

    2017-12-22

    CaFe_{2}O_{4} is an anisotropic S=5/2 antiferromagnet with two competing A (↑↑↓↓) and B (↑↓↑↓) magnetic order parameters separated by static antiphase boundaries at low temperatures. Neutron diffraction and bulk susceptibility measurements, show that the spins near these boundaries are weakly correlated and a carry an uncompensated ferromagnetic moment that can be tuned with a magnetic field. Spectroscopic measurements find these spins are bound with excitation energies less than the bulk magnetic spin waves and resemble the spectra from isolated spin clusters. Localized bound orphaned spins separate the two competing magnetic order parameters in CaFe_{2}O_{4}.

  3. Quantum chromodynamics, antiferromagnets and XY models from a unified point of view

    Directory of Open Access Journals (Sweden)

    Christoph P. Hofmann

    2017-03-01

    Full Text Available Antiferromagnets and quantum XY magnets in three space dimensions are described by an effective Lagrangian that exhibits the same structure as the effective Lagrangian of quantum chromodynamics with two light flavors. These systems all share a spontaneously broken internal symmetry O(N→O(N−1. Although the respective scales differ by many orders of magnitude, the general structure of the low-temperature expansion of the partition function is the same. In the nonabelian case (N≥3, logarithmic terms of the form T8ln⁡T emerge at three-loop order, while for N=2 the series only involves powers of T2. The manifestation of the Goldstone boson interaction in the pressure, order parameter, and susceptibility is explored in presence of an external field.

  4. The magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS3

    Science.gov (United States)

    Wildes, A. R.; Simonet, V.; Ressouche, E.; Ballou, R.; McIntyre, G. J.

    2017-11-01

    The magnetic properties and magnetic structure are presented for CoPS3, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Néel temperature of TN ∼120 K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2 K and 300 K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Single-crystal neutron diffraction shows that the magnetic propagation vector is k  =  (0 1 0) with the moments mostly along the {a} axis and with a small component along the {c} axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent 2β = 0.60 +/- 0.01 for T > 0.9~TN .

  5. Unifying static and dynamic properties in three-dimensional quantum antiferromagnets

    Science.gov (United States)

    Scammell, H. D.; Kharkov, Y.; Qin, Yan Qi; Meng, Zi Yang; Normand, B.; Sushkov, O. P.

    2017-11-01

    Quantum Monte Carlo simulations offer an unbiased means to study the static and dynamic properties of quantum critical systems, while quantum field theory provides direct analytical results. We study three-dimensional, critical quantum antiferromagnets by performing a combined analysis using both quantum field theory calculations and quantum Monte Carlo data. Explicitly, we analyze the order parameter (staggered magnetization), Néel temperature, quasiparticle gaps, and the susceptibilities in the scalar and vector channels. We connect the two approaches by deriving descriptions of the quantum Monte Carlo observables in terms of the quasiparticle excitations of the field theory. The remarkable agreement not only unifies the description of the static and dynamic properties of the system but also constitutes a thorough test of perturbative O(3) quantum field theory and opens new avenues for the analytical guidance of detailed numerical studies.

  6. Magnetic phase diagrams of classical triangular and kagome antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Gvozdikova, M V [Department of Physics, Kharkov National University, 61077 Kharkov (Ukraine); Melchy, P-E; Zhitomirsky, M E, E-mail: mike.zhitomirsky@cea.fr [Service de Physique Statistique, Magnetisme et Supraconductivite, UMR-E9001 CEA-INAC/UJF, 17 rue des Martyrs, 38054 Grenoble (France)

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  7. Role of the antiferromagnetic bulk spins in exchange bias

    Energy Technology Data Exchange (ETDEWEB)

    Schuller, Ivan K. [Center for Advanced Nanoscience and Physics Department, University of California San Diego, La Jolla, CA 92093 (United States); Morales, Rafael, E-mail: rafael.morales@ehu.es [Department of Chemical-Physics & BCMaterials, University of the Basque Country UPV/EHU (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain); Batlle, Xavier [Departament Física Fonamental and Institut de Nanociència i Nanotecnologia, Universitat de Barcelona, c/ Martí i Franqués s/n, 08028 Barcelona, Catalonia (Spain); Nowak, Ulrich [Department of Physics, University of Konstanz, 78464 Konstanz (Germany); Güntherodt, Gernot [Physics Institute (IIA), RWTH Aachen University, Campus RWTH-Melaten, 52074 Aachen (Germany)

    2016-10-15

    This “Critical Focused Issue” presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice. - Highlights: • We address the role of bulk antiferromagnetic spins in the exchange bias phenomenon. • Significant experiments on how bulk AFM spins determine exchange bias are highlighted. • We explain the model that accounts for experimental results.

  8. Spin Hall magnetoresistance in antiferromagnet/normal metal bilayers

    KAUST Repository

    Manchon, Aurelien

    2017-01-01

    We investigate the emergence of spin Hall magnetoresistance in a magnetic bilayer composed of a normal metal adjacent to an antiferromagnet. Based on a recently derived drift diffusion equation, we show that the resistance of the bilayer depends on the relative angle between the direction transverse to the current flow and the Néel order parameter. While this effect presents striking similarities with the spin Hall magnetoresistance recently reported in ferromagnetic bilayers, its physical origin is attributed to the anisotropic spin relaxation of itinerant spins in the antiferromagnet.

  9. 2D Multipartite Valence Bond States in Quantum Antiferromagnets

    CERN Document Server

    Rico, E

    2007-01-01

    A quantum anti-ferromagnetic spin-1 model is characterised on a 2D lattice with the following requirements: i) The Hamiltonian is made out of nearest neighbour interactions. ii) It is homogeneous, translational and rotational invariant. iii) The ground state is a real singlet state of SU(2) (non-chiral). iv) It has a local spin-1 representation. Along the way to characterise the system, connections with classical statistical mechanics and integrable models are explored. Finally, the relevance of the model in the physics of low dimensional anti-ferromagnetic Mott-Hubbard insulators is discussed.

  10. Spin waves in antiferromagnetic FeF2

    DEFF Research Database (Denmark)

    Hutchings, M T; Rainford, B.D.; Guggenheim, H J

    1970-01-01

    Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin Hamilton......Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin...

  11. Quantification of quantum discord in a antiferromagnetic Heisenberg compound

    Energy Technology Data Exchange (ETDEWEB)

    Singh, H., E-mail: chiranjib@iiserkol.ac.in; Chakraborty, T., E-mail: chiranjib@iiserkol.ac.in; Mitra, C., E-mail: chiranjib@iiserkol.ac.in [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, Mohanpur -741252, Nadia, West Bengal (India)

    2014-04-24

    An experimental quantification of concurrence and quantum discord from heat capacity (C{sub p}) measurement performed over a solid state system has been reported. In this work, thermodynamic measurements were performed on copper nitrate (CN, Cu(NO{sub 3}){sub 2}⋅2.5H{sub 2}O) single crystals which is an alternating antiferromagnet Heisenberg spin 1/2 system. CN being a weak dimerized antiferromagnet is an ideal system to investigate correlations between spins. The theoretical expressions were used to obtain concurrence and quantum discord curves as a function of temperature from heat capacity data of a real macroscopic system, CN.

  12. Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

    Directory of Open Access Journals (Sweden)

    Patta Ravikumar

    2015-08-01

    Full Text Available We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μB/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (TC around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high TC and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

  13. Monopoles in an Antiferromagnetic Bose-Einstein Condensate

    NARCIS (Netherlands)

    Stoof, H.T.C.; Vliegen, E.; Al Khawaja, U.

    2001-01-01

    We show that even in three dimensions an antiferromagnetic spin-1 Bose-Einstein condensate, which can, for instance, be created with 23Na atoms in an optical trap, has not only singular linelike vortex excitations, but also allows for singular pointlike topological excitations, i.e., monopoles

  14. Room-temperature antiferromagnetism in CuMnAs

    Energy Technology Data Exchange (ETDEWEB)

    Maca, F.; Masek, J. [Institute of Physics ASCR, v.v.i., Na Slovance 2, 182 21 Praha 8 (Czech Republic); Stelmakhovych, O. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Marti, X. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6 (Czech Republic); Reichlova, H. [Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6 (Czech Republic); Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Uhlirova, K. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Beran, P. [Nuclear Physics Institute ASCR, v.v.i., 250 68 Rez (Czech Republic); Wadley, P.; Novak, V. [Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6 (Czech Republic); Jungwirth, T., E-mail: jungw@fzu.cu [Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6 (Czech Republic); School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2012-04-15

    We report on an experimental and theoretical study of CuMn-V compounds. In agreement with previous works we find low-temperature antiferromagnetism with Neel temperature of 50 K in the cubic half-Heusler CuMnSb. We demonstrate that the orthorhombic CuMnAs is a room-temperature antiferromagnet. Our results are based on X-ray diffraction, magnetization, transport, and differential thermal analysis measurements, and on density-functional theory calculations of the magnetic structure of CuMn-V compounds. In the discussion part of the paper we make a prediction, based on our density-functional theory calculations, that the electronic structure of CuMn-V compounds makes a transition from a semimetal to a semiconductor upon introducing the lighter group-V elements. - Highlights: Black-Right-Pointing-Pointer We report experimental observation of high temperature antiferromagnetism in CuMnAs. Black-Right-Pointing-Pointer The physical origin of the observation is discussed based on ab initio calculations. Black-Right-Pointing-Pointer We predict semimetal to semiconductor transition of the electronic structure of CuMn-V compounds. Black-Right-Pointing-Pointer We discuss the relevance of CuMn-V compounds for antiferromagnetic spintronics.

  15. Observation of Antiferromagnetic Resonance in an Organic Superconductor

    DEFF Research Database (Denmark)

    Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.

    1982-01-01

    Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...

  16. Spin Transport and Dynamics in Antiferromagnetic Metals and Magnetic Insulators

    NARCIS (Netherlands)

    Swaving, A.C.|info:eu-repo/dai/nl/313938083

    2012-01-01

    It is demonstrated that in an antiferromagnetic metal a steady-state transport current generates a current-induced out-of-plane spin density, resulting in torques on the magnetization. This spin density is parameterized by a velocity that is proportional to the current. The generalization of the

  17. Ising antiferromagnet with mobile, pinned, and quenched defects

    Directory of Open Access Journals (Sweden)

    W.Selk

    2005-01-01

    Full Text Available Motivated by recent experiments on (Sr,Ca,La14Cu24O41, a two-dimensional Ising antiferromagnet with mobile, locally pinned and quenched defects is introduced and analyzed using mainly Monte Carlo techniques. The interplay between the arrangement of the defects and the magnetic ordering as well as the effect of an external field are studied.

  18. Current-induced torques in continuous antiferromagnetic textures

    NARCIS (Netherlands)

    Swaving, A.C.|info:eu-repo/dai/nl/313938083; Duine, R.A.|info:eu-repo/dai/nl/304830127

    2011-01-01

    We study the influence of an electric current on a continuous noncollinear antiferromagnetic texture. Despite the lack of a net magnetic moment, we find that the exchange interaction between conduction electrons and local magnetization generally results in current-induced torques that are nonzero

  19. Frustrated spin-1/2 molecular magnetism in the mixed-valence antiferromagnets Ba3M Ru2O9 (M =In , Y, Lu)

    Science.gov (United States)

    Ziat, D.; Aczel, A. A.; Sinclair, R.; Chen, Q.; Zhou, H. D.; Williams, T. J.; Stone, M. B.; Verrier, A.; Quilliam, J. A.

    2017-05-01

    We have performed magnetic susceptibility, heat capacity, muon spin relaxation, and neutron-scattering measurements on three members of the family Ba3M Ru2O9 , where M =In , Y, and Lu. These systems consist of mixed-valence Ru dimers on a triangular lattice with antiferromagnetic interdimer exchange. Although previous work has argued that charge order within the dimers or intradimer double exchange plays an important role in determining the magnetic properties, our results suggest that the dimers are better described as molecular units due to significant orbital hybridization, resulting in one spin-1/2 moment distributed equally over the two Ru sites. These molecular building blocks form a frustrated, quasi-two-dimensional triangular lattice. Our zero- and longitudinal-field μ SR results indicate that the molecular moments develop a collective, static magnetic ground state, with oscillations of the zero-field muon spin polarization indicative of long-range magnetic order in the Lu sample. The static magnetism is much more disordered in the Y and In samples, but they do not appear to be conventional spin glasses.

  20. Impact of anisotropy on antiferromagnet rotation in Heusler-type ferromagnet/antiferromagnet epitaxial bilayers

    Science.gov (United States)

    Hajiri, T.; Matsushita, M.; Ni, Y. Z.; Asano, H.

    2017-04-01

    We report the magnetotransport properties of ferromagnet (FM)/antiferromagnet (AFM) Fe2CrSi /Ru2MnGe epitaxial bilayers using current-in-plane configurations. Above the critical thickness of the Ru2MnGe layer to induce exchange bias, symmetric and asymmetric curves were observed in response to the direction of FM magnetocrystalline anisotropy. Because each magnetoresistance curve showed full and partial AFM rotation, the magnetoresistance curves imply the impact of the Fe2CrSi magnetocrystalline anisotropy to govern the AFM rotation. The maximum magnitude of the angular-dependent resistance-change ratio of the bilayers is more than an order of magnitude larger than that of single-layer Fe2CrSi films, resulting from the reorientation of AFM spins via the FM rotation. These results highlight the essential role of controlling the AFM rotation and reveal a facile approach to detect the AFM moment even in current-in-plane configurations in FM/AFM bilayers.

  1. Octa-Kagomé Lattice Compounds Showing Quantum Critical Behaviors: Spin Gap Ground State versus Antiferromagnetic Ordering.

    Science.gov (United States)

    Tang, Yingying; Peng, Cheng; Guo, Wenbin; Wang, Jun-Feng; Su, Gang; He, Zhangzhen

    2017-10-11

    Search for a new geometrically frustrated lattice is a great challenge. Herein, we report on a successful synthesis of two new layered compounds BiOCu2(XO3)(SO4)(OH)·H2O [X = Te (1) and Se (2)] with a new type of geometrically frustrated lattice (i.e., the octa-kagomé lattice) between kagomé and star motifs. Magnetic measurements confirmed that 1 exhibits a spin gap ground state, while 2 possesses a typical antiferromagnetic ordering at low-temperature. Such different magnetic behaviors between two isostructural compounds are suggested to originate from a slightly structural modification induced by nonmagnetic XO3 anionic groups. Theoretical simulations suggest that the origin of gapped ground state in 1 may be due to the dimerization of Cu2+ ions, while 2 may break the limiting of such dimerization, leading to an antiferromagnetic ordering.

  2. Sequential write-read operations in FeRh antiferromagnetic memory

    Science.gov (United States)

    Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo

    2015-09-01

    B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the Néel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-orderd FeRh thin films by a magnetic field and electric current only, which open a realistic pathway towards operational antiferromagnetic memory devices.

  3. Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP{sub 0.75}Si{sub 0.25} alloy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Guijiang, E-mail: guijiangli@gmail.com; Li, Wei; Schönecker, Stephan; Li, Xiaoqing [Applied Materials Physics, Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-10044 Stockholm (Sweden); Delczeg-Czirjak, Erna K.; Kvashnin, Yaroslav O.; Eriksson, Olle [Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Johansson, Börje [Applied Materials Physics, Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-10044 Stockholm (Sweden); Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Vitos, Levente [Applied Materials Physics, Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-10044 Stockholm (Sweden); Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, P.O. Box 49, Budapest H-1525 (Hungary)

    2014-12-29

    The magnetic state of the FeMnP{sub 0.75}Si{sub 0.25} alloy was investigated by first principles calculations. The coexistence of ferromagnetic and antiferromagnetic phases in FeMnP{sub 0.75}Si{sub 0.25} with the same hexagonal crystal structure was revealed. It was found that kinetic arrest during the transition from the high temperature disordered paramagnetic phase to the low temperature ordered ferromagnetic phase results in the intermediate metastable and partially disordered antiferromagnetic phase. We propose that the ratio of the ferromagnetic and antiferromagnetic phases in the FeMnP{sub 0.75}Si{sub 0.25} sample can be tuned by adjusting the kinetic process of atomic diffusion. The investigations suggest that careful control of the kinetic diffusion process provides another tuning parameter to design candidate magnetocaloric materials.

  4. Hypnosis, suggestion, and suggestibility: an integrative model.

    Science.gov (United States)

    Lynn, Steven Jay; Laurence, Jean-Roch; Kirsch, Irving

    2015-01-01

    This article elucidates an integrative model of hypnosis that integrates social, cultural, cognitive, and neurophysiological variables at play both in and out of hypnosis and considers their dynamic interaction as determinants of the multifaceted experience of hypnosis. The roles of these variables are examined in the induction and suggestion stages of hypnosis, including how they are related to the experience of involuntariness, one of the hallmarks of hypnosis. It is suggested that studies of the modification of hypnotic suggestibility; cognitive flexibility; response sets and expectancies; the default-mode network; and the search for the neurophysiological correlates of hypnosis, more broadly, in conjunction with research on social psychological variables, hold much promise to further understanding of hypnosis.

  5. Evidence of antiferromagnetic order in the green phases R sub 2 BaCuO sub 5 (R = Dy, Y, and Yb)

    Energy Technology Data Exchange (ETDEWEB)

    Salinas-Sanchez, A.; Saez-Puche, R.; Alario-Franco, M.A. (Universidad Complutense, Madrid (Spain))

    1990-12-01

    Magnetic susceptibility measurements between 4.2 and 300 K for R{sub 2}BaCuO{sub 5} compounds (R = Dy, Y and Yb), also called green phases, reveal the existence of antiferromagnetic ordering in the copper sublattice around 30 K. At lower temperatures {chi} vs. T plots show in all cases the existence of a sharp maximum, which can be attributed to the onset of antiferromagnetic ordering in the rare earth sublattice, probably induced by the polarization of Cu{sup +2} ions. Experimental magnetic moments estimated from the Curie-Weiss region generally agree with the theoretical values expected for thee R{sup +3} ions. High-resolution transmission electron microscopy and electron diffraction experiments confirm the earlier proposed structures for the R{sub 2}BaCuO{sub 5}, and show the existence of a well ordered material.

  6. Phase transitions and critical properties in the antiferromagnetic Ising model on a layered triangular lattice with allowance for intralayer next-nearest-neighbor interactions

    Energy Technology Data Exchange (ETDEWEB)

    Badiev, M. K., E-mail: m-zagir@mail.ru; Murtazaev, A. K.; Ramazanov, M. K. [Russian Academy of Sciences, Institute of Physics, Dagestan Scientific Center (Russian Federation)

    2016-10-15

    The phase transitions (PTs) and critical properties of the antiferromagnetic Ising model on a layered (stacked) triangular lattice have been studied by the Monte Carlo method using a replica algorithm with allowance for the next-nearest-neighbor interactions. The character of PTs is analyzed using the histogram technique and the method of Binder cumulants. It is established that the transition from the disordered to paramagnetic phase in the adopted model is a second-order PT. Static critical exponents of the heat capacity (α), susceptibility (γ), order parameter (β), and correlation radius (ν) and the Fischer exponent η are calculated using the finite-size scaling theory. It is shown that (i) the antiferromagnetic Ising model on a layered triangular lattice belongs to the XY universality class of critical behavior and (ii) allowance for the intralayer interactions of next-nearest neighbors in the adopted model leads to a change in the universality class of critical behavior.

  7. Fractional excitations in the square-lattice quantum antiferromagnet

    DEFF Research Database (Denmark)

    Piazza, B. Dalla; Mourigal, M.; Christensen, Niels Bech

    2015-01-01

    characterize the magnetic fluctuations in the metal-organic compound Cu(DCOO)(2)center dot 4D(2)O, a known realization of the quantum square-lattice Heisenberg antiferromagnet model. Our experiments reveal an isotropic excitation continuum at the anomaly, which we analyse theoretically using Gutzwiller......Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum...... square-lattice Heisenberg antiferromagnet, for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum. This quantum effect manifests itself for excitations propagating with the specific wavevector (pi,0). We use polarized neutron spectroscopy to fully...

  8. Role of the antiferromagnetic bulk spins in exchange bias

    Science.gov (United States)

    Schuller, Ivan K.; Morales, Rafael; Batlle, Xavier; Nowak, Ulrich; Güntherodt, Gernot

    2016-10-01

    This "Critical Focused Issue" presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice.

  9. Entanglement in a Spin-$s$ Antiferromagnetic Heisenberg Chain

    OpenAIRE

    Hao, Xiang; Zhu, Shiqun

    2006-01-01

    The entanglement in a general Heisenberg antiferromagnetic chain of arbitrary spin-$s$ is investigated. The entanglement is witnessed by the thermal energy which equals to the minimum energy of any separable state. There is a characteristic temperature below that an entangled thermal state exists. The characteristic temperature for thermal entanglement is increased with spin $s$. When the total number of lattice is increased, the characteristic temperature decreases and then approaches a cons...

  10. Spin Transport in Antiferromagnetic Insulators Mediated by Magnetic Correlations

    OpenAIRE

    Wang, Hailong; Du, Chunhui; Hammel, P. Chris; Yang, Fengyuan

    2015-01-01

    We report a systematic study of spin transport in antiferromagnetic (AF) insulators having a wide range of ordering temperatures. Spin current is dynamically injected from Y3Fe5O12 (YIG) into various AF insulators in Pt/insulator/YIG trilayers. Robust, long-distance spin transport in the AF insulators is observed, which shows strong correlation with the AF ordering temperatures. We find a striking linear relationship between the spin decay length in the AFs and the damping enhancement in YIG,...

  11. Effects of random fields in an antiferromagnetic Ising bilayer film

    Science.gov (United States)

    Kaneyoshi, T.

    2017-10-01

    The magnetic properties (phase diagrams and magnetizations) of an antiferromagnetic Ising bilayer film with random fields are investigated by the use of the effective field theory with correlations. It is examined how an uncompensated magnetization can be realized in the system, due to the effects of random fields in the two layers. They show the tricritical, compensation point and reentrant phenomena, depending on these parameters.

  12. Magnetization behavior of nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Loeffler, J.; Wagner, W.; Svygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Meier, J.; Doudin, B.; Ansermet, J.P. [Ecole Polytechnique Federale, Lausanne (Switzerland)

    1997-09-01

    The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs.

  13. Polarized Neutron Reflectivity Simulation of Ferromagnet/ Antiferromagnet Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki Yeon; Lee, Jeong Soo

    2008-02-15

    This report investigates the current simulating and fitting programs capable of calculating the polarized neutron reflectivity of the exchange-biased ferromagnet/antiferromagnet magnetic thin films. The adequate programs are selected depending on whether nonspin flip and spin flip reflectivities of magnetic thin films and good user interface are available or not. The exchange-biased systems such as Fe/Cr, Co/CoO, CoFe/IrMn/Py thin films have been simulated successfully with selected programs.

  14. Academic Meeting Scheduling Using an Antiferromagnetic Potts Model

    Science.gov (United States)

    Kudo, Kazue

    2017-07-01

    Scheduling parallel sessions of an academic meeting is a complicated task. If each presentation is assigned to an appropriate session, an antiferromagnetic Potts model can be used for semi-automatic timetabling. The timetabling method proposed here is based on graph coloring and includes additional constraints to be considered in a practical situation. We examine the feasibility of semi-automatic timetabling in some practical examples.

  15. Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

    Czech Academy of Sciences Publication Activity Database

    Galceran, R.; Fina, I.; Cisneros-Fernandez, J.; Bozzo, B.; Frontera, C.; Lopez-Mir, L.; Deniz, H.; Park, K.W.; Park, B.G.; Balcells, J.; Martí, Xavier; Jungwirth, Tomáš; Martínez, B.

    2016-01-01

    Roč. 6, Oct (2016), 1-6, č. článku 35471. ISSN 2045-2322 R&D Projects: GA MŠk LM2015087; GA ČR GB14-37427G EU Projects: European Commission(XE) 268066 - 0MSPIN Institutional support: RVO:68378271 Keywords : antiferromagnets * spintronics * magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.259, year: 2016

  16. Novel current driven domain wall dynamics in synthetic antiferromagnets

    Science.gov (United States)

    Yang, See-Hun

    It was reported that the domain walls in nanowires can be moved efficiently by electrical currents by a new type of torque, chiral spin torque (CST), the combination of spin Hall effect and Dzyaloshinskii-Moriya interaction. Recently we domonstrated that ns-long current pulses can move domain walls at extraordinarily high speeds (up to ~750 m s -1) in synthetic antiferromagnetic (SAF) nanowires that have almost zero net magnetization, which is much more efficient compared with similar nanowires in which the sub-layers are coupled ferromagnetically (SF). This high speed is found to be due to a new type of powerful torque, exchange coupling torque (ECT) that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers, showing that the ECT is effective only in SAF not in SF. Moreover, it is found that the dependence of the wall velocity on the magnetic field applied along the nanowire is non-monotonic. Most recently we predict an Walker-breakdown-like domain wall precession in SAF nanowires in the presence of in-plane field based on the model we develop, and this extraordinary precession has been observed. In this talk I will discuss this in details by showing a unique characteristics of SAF sublayers' DW boost-and-drag mechanism along with CST and ECT. Novel current driven domain wall dynamics in synthetic antiferromagnets.

  17. Ferromagnetic and antiferromagnetic orderings in wurtzite diluted magnetic nanostructures

    Science.gov (United States)

    Tronc, P.; Kitaev, Yu. E.; Hayn, R.; Strelchuk, V.; Kolomys, O.

    2017-10-01

    Using a new approach based on symmetry analysis, we have determined the magnetic symmetry groups (Shubnikov groups) of ferro- and antiferromagnetic wurtzite nanostructures doped with magnetic atoms periodically distributed at cation sites as well as the direction of the spontaneous magnetic field. Quantum wells, nanorods (nanowires), nanotubes, and quantum dots have been considered. The direction of the spontaneous magnetic field is determined by magnetic atoms with higher C3v (3m) or Cs (m) site symmetry group (the site symmetry group is defined with respect to the doped nanostructure). When the magnetic-atom distribution becomes more or less disordered (Diluted Magnetic Semiconductors), it seems reasonable to assume that, in most of the cases, the symmetry in regions with a size of some wurtzite unit-cells remains close to that of a periodic one, hence possibly inducing local ferro- or antiferromagnetic properties. The regions can induce overall ferro- or antiferromagnetic states when they have common spontaneous magnetic field direction or, possibly, induce easy-magnetization direction or plane (direction or plane of maximal magnetization intensity for a given external magnetic field strength) when disorder imposes a spread of spontaneous magnetic field direction over the various regions. Of course, such an effect adds itself to magnetic properties eventually induced by grain boundaries, other crystalline phases, and defects such as vacancies, dislocations or interstitial atoms.

  18. Enhanced Spin Conductance of a Thin-Film Insulating Antiferromagnet

    Science.gov (United States)

    Bender, Scott A.; Skarsvâg, Hans; Brataas, Arne; Duine, Rembert A.

    2017-08-01

    We investigate spin transport by thermally excited spin waves in an antiferromagnetic insulator. Starting from a stochastic Landau-Lifshitz-Gilbert phenomenology, we obtain the out-of-equilibrium spin-wave properties. In linear response to spin biasing and a temperature gradient, we compute the spin transport through a normal-metal-antiferromagnet-normal-metal heterostructure. We show that the spin conductance diverges as one approaches the spin-flop transition; this enhancement of the conductance should be readily observable by sweeping the magnetic field across the spin-flop transition. The results from such experiments may, on the one hand, enhance our understanding of spin transport near a phase transition, and on the other be useful for applications that require a large degree of tunability of spin currents. In contrast, the spin Seebeck coefficient does not diverge at the spin-flop transition. Furthermore, the spin Seebeck coefficient is finite even at zero magnetic field, provided that the normal metal contacts break the symmetry between the antiferromagnetic sublattices.

  19. Magnetic Transport in Spin Antiferromagnets for Spintronics Applications

    Directory of Open Access Journals (Sweden)

    Mohamed Azzouz

    2017-10-01

    Full Text Available Had magnetic monopoles been ubiquitous as electrons are, we would probably have had a different form of matter, and power plants based on currents of these magnetic charges would have been a familiar scene of modern technology. Magnetic dipoles do exist, however, and in principle one could wonder if we can use them to generate magnetic currents. In the present work, we address the issue of generating magnetic currents and magnetic thermal currents in electrically-insulating low-dimensional Heisenberg antiferromagnets by invoking the (broken electricity-magnetism duality symmetry. The ground state of these materials is a spin-liquid state that can be described well via the Jordan–Wigner fermions, which permit an easy definition of the magnetic particle and thermal currents. The magnetic and magnetic thermal conductivities are calculated in the present work using the bond–mean field theory. The spin-liquid states in these antiferromagnets are either gapless or gapped liquids of spinless fermions whose flow defines a current just as the one defined for electrons in a Fermi liquid. The driving force for the magnetic current is a magnetic field with a gradient along the magnetic conductor. We predict the generation of a magneto-motive force and realization of magnetic circuits using low-dimensional Heisenberg antiferromagnets. The present work is also about claiming that what the experiments in spintronics attempt to do is trying to treat the magnetic degrees of freedoms on the same footing as the electronic ones.

  20. Antiferromagnetic instability in Sr3Ru2O7: stabilized and revealed by dilute Mn impurities

    Science.gov (United States)

    Hossain, Muhammed; Bohnenbuck, B.; Chuang, Y.-D.; Cruz, E.; Wu, H.-H.; Tjeng, L. H.; Elfimov, I. S.; Hussain, Z.; Keimer, B.; Sawatzky, G. A.; Damascelli, A.

    2009-03-01

    X-ray Absorption Spectroscopy (XAS) and Resonant Elastic Soft X-ray Scattering (RESXS) studies have been performed on Mn-doped Sr3Ru2O7, both on the Ru and Mn L-edges, to investigate the origin of the metal insulator transition. Extensive simulations based on our experimental findings point toward an intrinsic antiferromagnetic instability in the parent Sr3Ru2O7 compound that is stabilized by the dilute Mn impurities. We show that the metal-insulator transition is a direct consequence of the antiferromagnetic order and we propose a phenomenological model that may be applicable also to metal-insulator transitions seen in other oxides. Moreover, a comparison of Ru and Mn L-edge data on 5% Mn doped system reveals that dilute Mn impurities are generating much more intense signal than Ru which is occupying 95% of the lattice sites. This suggests the embedding of dilute impurities as a powerful mean to probe weak and, possibly, spatially inhomogeneous order in solid-state systems. In collaboration with: Y. Yoshida (AIST), J. Geck, D.G. Hawthorn (UBC), M.W. Haverkort, Z. Hu, C. Sch"ußler-Langeheine (Cologne), R. Mathieu, Y. Tokura, S. Satow, H. Takagi (Tokyo), J.D. Denlinger (ALS).

  1. Fermi surface reconstruction and multiple quantum phase transitions in the antiferromagnet CeRhIn5

    Science.gov (United States)

    Jiao, Lin; Chen, Ye; Kohama, Yoshimitsu; Graf, David; Bauer, E. D.; Singleton, John; Zhu, Jian-Xin; Weng, Zongfa; Pang, Guiming; Shang, Tian; Zhang, Jinglei; Lee, Han-Oh; Park, Tuson; Jaime, Marcelo; Thompson, J. D.; Steglich, Frank; Si, Qimiao; Yuan, H. Q.

    2015-01-01

    Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas–van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs. PMID:25561536

  2. Tuning the ferromagnetic-antiferromagnetic interfaces of granular Co-CoO exchange bias systems by annealing

    Energy Technology Data Exchange (ETDEWEB)

    Menéndez, E., E-mail: Enric.MenendezDalmau@fys.kuleuven.be; Modarresi, H.; Pereira, L. M. C.; Temst, K.; Vantomme, A. [Instituut voor Kern- en Stralingsfysica, KU Leuven, Celestijnenlaan 200 D, BE-3001 Leuven (Belgium); Dias, T. [Instituut voor Kern- en Stralingsfysica, KU Leuven, Celestijnenlaan 200 D, BE-3001 Leuven (Belgium); Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, 91501-970 Rio Grande do Sul (Brazil); Geshev, J. [Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, 91501-970 Rio Grande do Sul (Brazil)

    2014-04-07

    The low-temperature magnetic behavior of granular Co-CoO exchange bias systems, prepared by oxygen ion implantation in Co thin films and subsequent annealing, is addressed. The thermal activation effects lead to an O migration which results in virtually pure Co areas embedded in a structurally relaxed and nearly stoichiometric CoO phase. This yields decreased training and exchange bias shifts, while the blocking temperature significantly increases, coming close to the Néel temperature of bulk CoO for samples implanted to a fluence above 1 × 10{sup 17} ions/cm{sup 2} (15% O). The dependence of the exchange bias shift on the pristine O-implanted content is analogous to that of the antiferromagnetic thickness in most ferromagnetic/antiferromagnetic systems (i.e., an increase in the exchange bias shift up to a maximum followed by a decrease until a steady state is reached), suggesting that, after annealing, the enriched Co areas might be rather similar in size for samples implanted above 1 × 10{sup 17} ions/cm{sup 2}, whereas the corresponding CoO counterparts become enlarged with pristine O content (i.e., effect of the antiferromagnet size). This study demonstrates that the magnetic properties of granular Co-CoO systems can be tailored by controllably modifying the local microstructure through annealing treatments.

  3. Open to Suggestion.

    Science.gov (United States)

    Journal of Reading, 1987

    1987-01-01

    Offers (1) suggestions for improving college students' study skills; (2) a system for keeping track of parent, teacher, and community contacts; (3) suggestions for motivating students using tic tac toe; (4) suggestions for using etymology to improve word retention; (5) a word search grid; and (6) suggestions for using postcards in remedial reading…

  4. Spin liquids and antiferromagnetic order in the Shastry-Sutherland-lattice compound Yb2Pt2Pb.

    Science.gov (United States)

    Kim, M S; Aronson, M C

    2013-01-04

    We present measurements of the magnetic susceptibility χ and the magnetization M of single crystals of metallic Yb(2)Pt(2)Pb, where localized Yb moments lie on the dimerized and frustrated Shastry-Sutherland lattice (SSL). Strong magnetic frustration is found in this quasi-two-dimensional system, which orders antiferromagnetically at T(N) = 2.02 K from a paramagnetic liquid of Yb dimers, having a gap Δ = 4.6 K between the singlet ground state and the triplet excited states. Magnetic fields suppress the antiferromagnetic (AF) order, which vanishes at a 1.23 T quantum critical point. The spin gap Δ persists to 1.5 T, indicating that dimer singlets survive the collapse of the B = 0 AF state. Quantized steps are observed in M(B) within the AF state, a signature of SSL systems. Our results show that Yb(2) Pt(2)Pb is unique, both as a metallic SSL system that is close to an AF quantum critical point, and as a heavy fermion compound where quantum frustration plays a decisive role.

  5. Crystal structure and characterization of a novel layered copper-lithium phosphonate with antiferromagnetic intrachain Cu(II)···Cu(II) interactions

    Energy Technology Data Exchange (ETDEWEB)

    Abdelbaky, Mohammed S.M. [Departments of Physical and Analytical Chemistry and Organic and Inorganic Chemistry, University of Oviedo-CINN, 33006 Oviedo (Spain); Amghouz, Zakariae [Scientific and Technical Services, University of Oviedo-CINN, 33006 Oviedo (Spain); Department of Materials Science and Metallurgical Engineering, University of Oviedo, Campus Universitario, 33203 Gijón (Spain); Blanco, David Martínez [Scientific and Technical Services, University of Oviedo-CINN, 33006 Oviedo (Spain); García-Granda, Santiago; García, José R. [Departments of Physical and Analytical Chemistry and Organic and Inorganic Chemistry, University of Oviedo-CINN, 33006 Oviedo (Spain)

    2017-04-15

    Novel metal phosphonate [CuLi(PPA)] [H{sub 3}PPA=3-phosphonopropionic acid] was synthesized hydrothermally and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis. It crystallizes in the space group C2/c, with cell parameters a=21.617(2) Å, b=4.9269(2) Å, c=14.342(1) Å, β=132.3(2)°, and Z=8. Its framework is built up from a main trimer, acting as a secondary building unit (SBU), which is formed by vertex-shared between two (LiO{sub 4}) and one (Cu(1)O{sub 4}) polyhedra. These units repeat along b-axis forming infinite inorganic chains, these chains are in turn cross-linked by corner sharing with (Cu(2)O{sub 4}) polyhedra to produce inorganic layers lying in the bc-plane. The neighboring layers are connected through the PPA ligand, leading to a 3D pillared-layered structure. The topological analysis reveals that the compound exhibits 3,4,10-c net. Finally, magnetic susceptibility measurement of this compound over the temperature range of 2–300 K reveals the occurrence of weak antiferromagnetic intrachain interactions. - Graphical abstract: Hydrothermal synthesis and structural characterization of a novel lithium-copper phosphonate, formulated as [CuLi(PPA)] (H{sub 3}PPA=3-phosphonopropionic acid), have been reported. This compound has a 3D pillared-layered structure with 3,4,10-c net topology. The magnetic susceptibility data over the temperature range of 2–300 K reveals the occurrence of weak antiferromagnetic interactions. - Highlights: • Novel metal phosphonate, [CuLi(PPA)] (1), has been synthesized and characterized. • Compound 1 has a 3D pillared-layered structure with 3,4,10-c net topology. • Magnetic susceptibility data reveals the occurrence of weak antiferromagnetic interactions.

  6. Weak Ferromagnetic Response of d Electrons and Antiferromagnetic Response of π Electrons in TPP[Mn(Pc)(CN)2]2 in Torque Magnetometry Experiments

    Science.gov (United States)

    Torizuka, Kiyoshi; Uwatoko, Yoshiya; Matsuda, Masaki; Yoshida, Gosuke; Kimata, Motoi; Tajima, Hiroyuki

    2017-11-01

    We have investigated the magnetic properties of TPP[Mn(Pc)(CN)2]2 by the cantilever magnetometry technique. This technique enables us to extract information on the magnetism even if the sample is very small (1 µg). The torque curve measured when the magnetic field (≤7 T) is rotated in a plane that includes the c-axis shows a signature that is characteristic of weak ferromagnetism. The electron responsible for this behavior should be the d electron of the Mn3+ ion. On the other hand, when the field is rotated in the ab-plane, the torque curve exhibits an antiferromagnetic signature. The electron responsible for this behavior should be the π electron. Taking the susceptibility data into account, we have proposed two models of the spin configuration for d electrons: canted antiferromagnetism, and the field-induced ferromagnetic alignment. We have pointed out that even in the canted antiferromagnetic case, the torque curve is the same as that in the ferromagnetic case if the anisotropy energy is very small. These models do not contradict the experimental observation that magnetoresistance is hardly seen in TPP[Mn(Pc)(CN)2]2 if the interaction between π and d electrons is weak.

  7. Antiferromagnetic structure in tetragonal CuMnAs thin films

    Science.gov (United States)

    Wadley, P.; Hills, V.; Shahedkhah, M. R.; Edmonds, K. W.; Campion, R. P.; Novák, V.; Ouladdiaf, B.; Khalyavin, D.; Langridge, S.; Saidl, V.; Nemec, P.; Rushforth, A. W.; Gallagher, B. L.; Dhesi, S. S.; Maccherozzi, F.; Železný, J.; Jungwirth, T.

    2015-11-01

    Tetragonal CuMnAs is an antiferromagnetic material with favourable properties for applications in spintronics. Using a combination of neutron diffraction and x-ray magnetic linear dichroism, we determine the spin axis and magnetic structure in tetragonal CuMnAs, and reveal the presence of an interfacial uniaxial magnetic anisotropy. From the temperature-dependence of the neutron diffraction intensities, the Néel temperature is shown to be (480 ± 5) K. Ab initio calculations indicate a weak anisotropy in the (ab) plane for bulk crystals, with a large anisotropy energy barrier between in-plane and perpendicular-to-plane directions.

  8. High-field spin dynamics of antiferromagnetic quantum spin chains

    DEFF Research Database (Denmark)

    Enderle, M.; Regnault, L.P.; Broholm, C.

    2000-01-01

    The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...

  9. Propagation and Ghosts in the Classical Kagome Antiferromagnet

    Science.gov (United States)

    Robert, J.; Canals, B.; Simonet, V.; Ballou, R.

    2008-09-01

    We investigate the classical spin dynamics of the kagome antiferromagnet by combining Monte Carlo and spin dynamics simulations. We show that this model has two distinct low temperature dynamical regimes, both sustaining propagative modes. The expected gauge invariance type of the low energy, low temperature, out-of-plane excitations is also evidenced in the nonlinear regime. A detailed analysis of the excitations allows us to identify ghosts in the dynamical structure factor, i.e., propagating excitations with a strongly reduced spectral weight. We argue that these dynamical extinction rules are of geometrical origin.

  10. Domain-Wall Spin Dynamics in Kagome Antiferromagnets

    Science.gov (United States)

    Lhotel, E.; Simonet, V.; Ortloff, J.; Canals, B.; Paulsen, C.; Suard, E.; Hansen, T.; Price, D. J.; Wood, P. T.; Powell, A. K.; Ballou, R.

    2011-12-01

    We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.

  11. Superparamagnetic behavior of antiferromagnetic six lines ferrihydrite nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Rani, Chandni, E-mail: chandni@thapar.edu; Tiwari, S.D.

    2017-05-15

    Magnetic behavior of 5 nm antiferromagnetic six lines ferrihydrite particles is reported. The magnetization as a function of applied magnetic field data at 100 K are fitted to the modified Langevin function without and with considering a distribution in particle magnetic moment covering different ranges of applied magnetic field strength. The resulting fit parameters are analyzed and compared. In the first case fit parameters are found to be strongly dependent on the strength of applied magnetic field. But the fit parameters are found to be independent of applied magnetic field strength in the later case.

  12. Antiferromagnetic phase transition and spin correlations in NiO

    DEFF Research Database (Denmark)

    Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker

    2009-01-01

    We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested...... by the strong diffuse magnetic scattering persist well above TN530 K and could still be observed at T=800 K which is about 1.5TN. We argue that the strong spin correlations above TN are due to the topological frustration of the spins on a fcc lattice. The Néel temperature is substantially reduced...

  13. Surface-induced phenomena in uncompensated collinear antiferromagnets.

    Science.gov (United States)

    Charilaou, M; Hellman, F

    2015-03-04

    The net spontaneous magnetization of antiferromagnets with modified surfaces was computed using mean-field theory. For ordinary phase transitions the net magnetization of uncompensated AFM is smaller than the surface magnetization and the Néel vector, whereas for extraordinary phase transitions the net magnetization is larger than the surface magnetization and the Néel vector at finite temperature. Moreover, the temperature dependence of these three observable internal parameters changes drastically with the surface properties, i.e. the surface exchange coupling JS. Based on these findings, contour plots showing different regions of magnetization and Néel vector behavior as functions of temperature and surface exchange strength are proposed.

  14. Possible Frustration Effects on a New Antiferromagnetic Compound Ce6Pd13Zn4 with the Octahedral Ce Sublattice

    Science.gov (United States)

    Matsuoka, Eiichi; Oshima, Akihiro; Sugawara, Hitoshi; Sakurai, Takahiro; Ohta, Hitoshi

    2018-01-01

    Magnetization, specific heat, and electrical resistivity measurements have been performed on polycrystalline samples of a new cubic compound, Ce6Pd13Zn4. This compound exhibits metallic behavior and is classified as a Kondo-lattice system. The trivalent Ce ions are responsible for the antiferromagnetic transition at TN = 3.3 K and the phase transition at T'N = 1.3 K with the formation of superzone gaps. The increase in magnetic susceptibilities below TN and the considerably large value of the specific heat divided by temperature (1.25 J·Ce-mol-1·K-2) imply the existence of non-ordered Ce magnetic moments due to the geometrical frustration on the octahedral Ce sublattice.

  15. Influence of the biquadratic exchange interaction in the classical ground state magnetic response of the antiferromagnetic icosahedron

    Science.gov (United States)

    Konstantinidis, N. P.

    2016-11-01

    The icosahedron has a ground state magnetization discontinuity in an external magnetic field when classical spins mounted on its vertices are coupled according to the antiferromagnetic Heisenberg model. This is so even if there is no magnetic anisotropy in the Hamiltonian. The discontinuity is a consequence of the frustrated nature of the interactions, which originates in the topology of the cluster. Here it is found that the addition of the next order isotropic spin exchange interaction term in the Hamiltonian, the biquadratic exchange interaction, significantly enriches the classical ground state magnetic response. For relatively weak biquadratic interaction new discontinuities emerge, while for even stronger the number of discontinuities for this small molecule can go up to seven, accompanied by a susceptibility discontinuity. These results demonstrate the possibility of using a small entity like the icosahedron as a magnetic unit whose ground state spin configuration and magnetization can be tuned between many different non-overlapping regimes with the application of an external field.

  16. Floating-zone growth and characterization of triangular lattice antiferromagnetic α-SrCr2O4 crystals

    Science.gov (United States)

    Zhao, Li; Wang, Kuen-Jen; Wen, Min-Hsueh; Wu, Maw-Kuen

    2014-04-01

    The triangular S=3/2 antiferromagnetic α-phase MCr2O4 (M=Ca, Sr, Ba) family has received increasing attention for their low dimensional geometrically frustrated magnetism. For the first time, the single crystals of α-SrCr2O4 were successfully grown by the floating-zone method. The plate-like crystals are highly a-axis oriented with a 60° twinning structure in the bc plane. We also investigated the magnetic susceptibilities, specific heat and dielectric properties systematically. Our results confirm a long range magnetic ordering emerging in α-SrCr2O4 below about 43 K. These crystals are suitable for the future neutron scattering experiments and other in-depth physical measurements.

  17. Superconductivity mediated by quantum critical antiferromagnetic fluctuations: The rise and fall of hot spots

    Science.gov (United States)

    Wang, Xiaoyu; Schattner, Yoni; Berg, Erez; Fernandes, Rafael M.

    2017-05-01

    In several unconventional superconductors, the highest superconducting transition temperature Tc is found in a region of the phase diagram where the antiferromagnetic transition temperature extrapolates to zero, signaling a putative quantum critical point. The elucidation of the interplay between these two phenomena—high-Tc superconductivity and magnetic quantum criticality—remains an important piece of the complex puzzle of unconventional superconductivity. In this paper, we combine sign-problem-free quantum Monte Carlo simulations and field-theoretical analytical calculations to unveil the microscopic mechanism responsible for the superconducting instability of a general low-energy model, called the spin-fermion model. In this approach, low-energy electronic states interact with each other via the exchange of quantum critical magnetic fluctuations. We find that even in the regime of moderately strong interactions, both the superconducting transition temperature and the pairing susceptibility are governed not by the properties of the entire Fermi surface, but instead by the properties of small portions of the Fermi surface called hot spots. Moreover, Tc increases with increasing interaction strength, until it starts to saturate at the crossover from hot-spots-dominated to Fermi-surface-dominated pairing. Our work provides not only invaluable insights into the system parameters that most strongly affect Tc, but also important benchmarks to assess the origin of superconductivity in both microscopic models and actual materials.

  18. Molecule-Based Magnets: Ferro- and Antiferromagnetic Interactions in Copper(II)-Polyorganosiloxanolate Clusters.

    Science.gov (United States)

    Rentschler, Eva; Gatteschi, Dante; Cornia, Andrea; Fabretti, Antonio C.; Barra, Anne-Laure; Shchegolikhina, Olga I.; Zhdanov, Alexandr A.

    1996-07-17

    The magnetic behavior of the clusters [(PhSiO(2))(6)Cu(6)(O(2)SiPh)(6)].6EtOH (1), Na(4)[(PhSiO(2))(12)Cu(4)].8(n)()BuOH (2), and K(4)[(C(2)H(3)SiO(2))(12)Cu(4)].6(n)()BuOH (3) has been investigated by combined magnetic susceptibility measurements and variable-temperature EPR techniques (9.25 and 245 GHz). The six copper(II) ions in the core of 1, which approaches 6/mmm symmetry, are ferromagnetically coupled as a result of the geometry at the bridging siloxanolate oxygen atoms (Cu-O-Cu = 91.5-94.6 degrees; J = -42 cm(-)(1) with H = J S(i)().S(i)()(+1), S(7) = S(1)). The ground S = 3 spin state is split in zero field mainly due to anisotropic exchange contributions (D = 0.30 cm(-)(1)). Notably, both the magnitude and the sign of the zero-field splitting parameter have been determined from HF-EPR spectra. Large antiferromagnetic Cu-Cu interactions (J approximately 200 cm(-)(1)) and an S = 0 ground state have been detected in the tetranuclear clusters 2 and 3 as a consequence of the larger Cu-O-Cu angles. The results presented in the paper are relevant to the search for new molecule-based magnetic materials.

  19. Effect of a nonmagnetic impurity in a nearly antiferromagnetic Fermi liquid: Magnetic correlations and transport phenomena

    Science.gov (United States)

    Kontani, Hiroshi; Ohno, Masanori

    2006-07-01

    In nearly antiferromagnetic (AF) metals such as high- Tc superconductors (HTSCs), a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GVI -FLEX method. This model corresponds to the HTSC with dilute nonmagnetic impurity concentration. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local density of states are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the “huge residual resistivity” beyond the s -wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong k -dependence due to non- s -wave scatterings induced by many-body effects, so the structure of the “hot spot/cold spot” in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can cause a “Kondo-like” upturn of resistivity (dρ/dTheavy fermion systems and organic superconductors.

  20. Manufacturer's Suggested Retail Prices

    NARCIS (Netherlands)

    Rosenkranz, S.|info:eu-repo/dai/nl/157222241

    2003-01-01

    Based on arguments of the `reference- dependent' theory of consumer choice we assume that a retailer's discount of a manufacturer's suggested retail price changes consumers' demand. We can show that the producer benefits from suggesting a retail price. If consumers are additionally sufficiently

  1. Strain fields and electronic structure of antiferromagnetic CrN

    Science.gov (United States)

    Rojas, Tomas; Ulloa, Sergio E.

    2017-09-01

    We present a theoretical analysis of the role that strain plays on the electronic structure of chromium nitride (CrN) crystals. We use local spin-density approximation + U calculations to study the elastic constants, deformation potentials, and strain dependence of electron and hole masses near the fundamental gap. We consider the lowest energy antiferromagnetic models believed to describe CrN at low temperatures, and apply strain along different directions. We find relatively large deformation potentials for all models, and find increasing gaps for tensile strain along most directions. Most interestingly, we find that compressive strains should be able to close the relatively small indirect gap (≃100 meV) at moderate amplitudes ≃1.3 % . We also find large and anisotropic changes in the effective masses with strain, with principal axes closely related to the magnetic ordering of neighboring layers in the antiferromagnet. It would be interesting to consider the role that these effects may have on typical film growth on different substrates, and the possibility of monitoring optical and transport properties of thin films as strain is applied.

  2. Spin-orbit torque in two dimensional antiferromagnetic topological insulators

    Science.gov (United States)

    Ghosh, Sumit; Manchon, Aurelien

    Topological insulators (TI) have been found to be a source of huge spin-orbit torque (SOT) that originates from their surface states. However, the proximity of a ferromagnetic layer can destroy the surface states which makes the exact nature of the SOT quite argumentative. Recently it has been found that in presence of an antiferromagnetic magnetization, a TI can preserve its gapless states. We conduct a systematic study on two-dimensional antiferromagnetic TI and find that they are more robust compared to a ferromagnetic TI against impurity scattering. It can facilitate a field like SOT due to the intrinsic spin-orbit coupling and an antidamping SOT via scattering by scalar impurity. Interestingly, a moderate amount of impurity enhances the staggered spin density at the edges resulting in a uniform antidamping torque with the conductance remaining finite. It is, therefore, possible to manipulate the magnetization either by using a pulse via field like SOT or by a dc current via antidamping SOT. This work was supported by the King Abdullah Uni- versity of Science and Technology (KAUST) through the Office of Sponsored Research (OSR) [Grant Number OSR-2015- CRG4-2626].

  3. Antiferromagnetic Kondo lattice compound CePt3P.

    Science.gov (United States)

    Chen, Jian; Wang, Zhen; Zheng, Shiyi; Feng, Chunmu; Dai, Jianhui; Xu, Zhu'an

    2017-02-03

    A new ternary platinum phosphide CePt3P was synthesized and characterized by means of magnetic, thermodynamic and transport measurements. The compound crystallizes in an antiperovskite tetragonal structure similar to that in the canonical family of platinum-based superconductors APt3P (A = Sr, Ca, La) and closely related to the noncentrosymmetric heavy fermion superconductor CePt3Si. In contrast to all the superconducting counterparts, however, no superconductivity is observed in CePt3P down to 0.5 K. Instead, CePt3P displays a coexistence of antiferromagnetic ordering, Kondo effect and crystalline electric field effect. A field-induced spin-flop transition is observed below the magnetic ordering temperature TN1 of 3.0 K while the Kondo temperature is of similar magnitude as TN1. The obtained Sommerfeld coefficient of electronic specific heat is γCe = 86 mJ/mol·K2 indicating that CePt3P is a moderately correlated antiferromagnetic Kondo lattice compound.

  4. Symmetry breaking and finite size scaling in antiferromagnets

    Science.gov (United States)

    Azaria, P.; Delamotte, B.; Mouhanna, D.

    1993-02-01

    We show that the finite size scaling analysis of the quantum non linear sigma model O(3)/O(2) associated with antiferromagnets justifies the existence of the tower of excited states first proposed by Anderson to explain the symmetry breaking of quantum antiferromagnets in the thermodynamical limit. Finite size formulas for the ground state energy and for the ground state expectation value of the order parameter are explicitly given. Nous montrons que l'analyse du comportement à taille finie du modèle sigma non linéaire quantique O(3)/O(2) adapté aux antiferromagnétiques justifie l'existence d'une tour d'états excités proposée pour la première fois par Anderson pour expliquer la brisure de symétrie des antiferromagnétiques quantiques dans la limite thermodynamique. Nous donnons également les formules de taille finie pour l'énergie du fondamental et pour la valeur moyenne dans le vide du paramètre d'ordre.

  5. Anisotropic Magnetoresistance in Antiferromagnetic Sr_{2}IrO_{4}

    Directory of Open Access Journals (Sweden)

    C. Wang

    2014-11-01

    Full Text Available We report point-contact measurements of anisotropic magnetoresistance (AMR in a single crystal of antiferromagnetic Mott insulator Sr_{2}IrO_{4}. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature reveal negative magnetoresistances (up to 28% for modest magnetic fields (250 mT applied within the IrO_{2} a-b plane and electric currents flowing perpendicular to the plane. The angular dependence of magnetoresistance shows a crossover from fourfold to twofold symmetry in response to an increasing magnetic field with angular variations in resistance from 1% to 14%. We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of antiferromagnetic-coupled moments in Sr_{2}IrO_{4}. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys or oxides (0.1%–0.5% and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order, and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion.

  6. Antiferromagnetic exchange bias of a ferromagnetic semiconductor by a ferromagnetic metal

    Energy Technology Data Exchange (ETDEWEB)

    Olejnik, K.; Wadley, P.; Haigh, J.; Edmonds, K. W.; Campion, R. P.; Rushforth, A. W.; Gallagher, B. L.; Foxon, C. T.; Jungwirth, T.; Wunderlich, J.; Dhesi, S. S.; Cavill, S.; van der Laan, G.; Arenholz, E.

    2009-11-05

    We demonstrate an exchange bias in (Ga,Mn)As induced by antiferromagnetic coupling to a thin overlayer of Fe. Bias fields of up to 240 Oe are observed. Using element-specific x-ray magnetic circular dichroism measurements, we distinguish an interface layer that is strongly pinned antiferromagnetically to the Fe. The interface layer remains polarized at room temperature.

  7. Development of antiferromagnetic Heusler alloys for the replacement of iridium as a critically raw material

    Science.gov (United States)

    Hirohata, Atsufumi; Huminiuc, Teodor; Sinclair, John; Wu, Haokaifeng; Samiepour, Marjan; Vallejo-Fernandez, Gonzalo; O'Grady, Kevin; Balluf, Jan; Meinert, Markus; Reiss, Günter; Simon, Eszter; Khmelevskyi, Sergii; Szunyogh, Laszlo; Yanes Díaz, Rocio; Nowak, Ulrich; Tsuchiya, Tomoki; Sugiyama, Tomoko; Kubota, Takahide; Takanashi, Koki; Inami, Nobuhito; Ono, Kanta

    2017-11-01

    As a platinum group metal, iridium (Ir) is the scarcest element on the earth but it has been widely used as an antiferromagnetic layer in magnetic recording, crucibles and spark plugs due to its high melting point. In magnetic recording, antiferromagnetic layers have been used to pin its neighbouring ferromagnetic layer in a spin-valve read head in a hard disk drive for example. Recently, antiferromagnetic layers have also been found to induce a spin-polarised electrical current. In these devices, the most commonly used antiferromagnet is an Ir-Mn alloy because of its corrosion resistance and the reliable magnetic pinning of adjacent ferromagnetic layers. It is therefore crucial to explore new antiferromagnetic materials without critical raw materials. In this review, recent research on new antiferromagnetic Heusler alloys and their exchange interactions along the plane normal is discussed. These new antiferromagnets are characterised by very sensitive magnetic and electrical measurement techniques recently developed to determine their characteristic temperatures together with atomic structural analysis. Mn-based alloys and compounds are found to be most promising based on their robustness against atomic disordering and large pinning strength up to 1.4 kOe, which is comparable with that for Ir-Mn. The search for new antiferromagnetic films and their characterisation are useful for further miniaturisation and development of spintronic devices in a sustainable manner.

  8. Suggestive Objects at Work

    DEFF Research Database (Denmark)

    Ratner, Helene Gad

    2009-01-01

    In Western secular societies, spiritual life is no longer limited to classical religious institutions but can also be found at workplace organizations. While spirituality is conventionally understood as a subjective and internal process, this paper proposes the concept of ‘suggestive objects’, co...... scaffolding. This has deep implications for our understanding of the sacred, including a better appreciation of the way that suggestive objects make the sacred durable, the way they organize it....

  9. Suggestive techniques in advertising

    OpenAIRE

    Sora, Olena

    2011-01-01

    In my thesis I focused on a detailed analysis of suggestive techniques that appear in contemporary advertising. The issue of the effects of advertising has existed for many years and still staying timely. On the one side there are entrepreneurs and advertising agencies that are trying to influence opinions and suggest motivation for consuming. On the other side there is a potential customer, who is trying to obtain information about the product he needs and at the same time not letting anybod...

  10. [Psychoanalysis and suggestion].

    Science.gov (United States)

    Thomä, H

    1977-01-01

    In the history of psychoanalysis the problem of suggestion has been a central one. At first it involved the necessity to establish the psychoanalytic technique as independent scientific paradigm in contrast to persuasion and hypnosis. However, it was not only the symptom-oriented suggestion that had to be given up for scientific reasons and reasons of treatment technique. Since professional and human factors as well could have influenced the psychoanalytic situation to revert to the traditional "suggestion", Freud has given some technical considerations (e.g. the mirror-analogy), that were meant to counteract the confusion of the psychoanalytic technique with the persuasive one that had to come up to late. The discovery of the transference phenomena has further complicated the problem. It became obvious that the capacity of the analyst to exert an influence and to have impact, originated in very basic human categories and their specific psychogenetic developments and distortions. This understanding contributed to the development of psychoanalytic theories of suggestibility. Until the present day the discovery of the transference phenomena has determined the discussions of psychoanalytic technique in term of the relationship between the special and general therapeutic factors (i.e. interpretation versus relationship). The departure from the therapeutic mode of persuasive suggestion and the introduction of psychoanalytic technique signaled the revolutionary paradigm of Sigmund Freud, i.e. the active participation of the patient and the process of observation. Often scientific problems related to this pradigm and suggestion are discussed concurrently.

  11. Spin transfer torque in antiferromagnetic spin valves: From clean to disordered regimes

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed

    2014-05-28

    Current-driven spin torques in metallic spin valves composed of antiferromagnets are theoretically studied using the nonequilibrium Green\\'s function method implemented on a tight-binding model. We focus our attention on G-type and L-type antiferromagnets in both clean and disordered regimes. In such structures, spin torques can either rotate the magnetic order parameter coherently (coherent torque) or compete with the internal antiferromagnetic exchange (exchange torque). We show that, depending on the symmetry of the spin valve, the coherent and exchange torques can either be in the plane, ∝n×(q×n) or out of the plane ∝n×q, where q and n are the directions of the order parameter of the polarizer and the free antiferromagnetic layers, respectively. Although disorder conserves the symmetry of the torques, it strongly reduces the torque magnitude, pointing out the need for momentum conservation to ensure strong spin torque in antiferromagnetic spin valves.

  12. Measuring Children's Suggestibility in Forensic Interviews.

    Science.gov (United States)

    Volpini, Laura; Melis, Manuela; Petralia, Stefania; Rosenberg, Melina D

    2016-01-01

    According to the scientific literature, childrens' cognitive development is not complete until adolescence. Therefore, the problems inherent in children serving as witnesses are crucial. In preschool-aged children, false memories may be identified because of misinformation and insight bias. Additionally, they are susceptible of suggestions. The aim of this study was to verify the levels of suggestibility in children between three and 5 years of age. Ninety-two children were examined (44 male, 48 female; M = 4.5 years, SD = 9.62). We used the correlation coefficient (Pearson's r) and the averages variance by SPSS statistical program. The results concluded that: younger children are almost always more susceptible to suggestibility. The dimension of immediate recall was negatively correlates with that of total suggestibility (r = -0.357 p Forensic Sciences.

  13. Open to Suggestion.

    Science.gov (United States)

    Journal of Reading, 1986

    1986-01-01

    Offers (1) suggestions on how to teach students the importance of regular study habits for learning to spell, (2) story ideas to help students get started with creative writing, and (3) a model of a daily record assignment book to help students organize and remember their homework assignments. (SRT)

  14. Antiferromagnetic nano-oscillator in external magnetic fields

    Science.gov (United States)

    Checiński, Jakub; Frankowski, Marek; Stobiecki, Tomasz

    2017-11-01

    We describe the dynamics of an antiferromagnetic nano-oscillator in an external magnetic field of any given time distribution. The oscillator is powered by a spin current originating from spin-orbit effects in a neighboring heavy metal layer and is capable of emitting a THz signal in the presence of an additional easy-plane anisotropy. We derive an analytical formula describing the interaction between such a system and an external field, which can affect the output signal character. Interactions with magnetic pulses of different shapes, with a sinusoidal magnetic field and with a sequence of rapidly changing magnetic fields are discussed. We also perform numerical simulations based on the Landau-Lifshitz-Gilbert equation with spin-transfer torque effects to verify the obtained results and find a very good quantitative agreement between analytical and numerical predictions.

  15. Antiferromagnetic Ising model in an imaginary magnetic field

    Science.gov (United States)

    Azcoiti, Vicente; Di Carlo, Giuseppe; Follana, Eduardo; Royo-Amondarain, Eduardo

    2017-09-01

    We study the two-dimensional antiferromagnetic Ising model with a purely imaginary magnetic field, which can be thought of as a toy model for the usual θ physics. Our motivation is to have a benchmark calculation in a system which suffers from a strong sign problem, so that our results can be used to test Monte Carlo methods developed to tackle such problems. We analyze here this model by means of analytical techniques, computing exactly the first eight cumulants of the expansion of the effective Hamiltonian in powers of the inverse temperature, and calculating physical observables for a large number of degrees of freedom with the help of standard multiprecision algorithms. We report accurate results for the free energy density, internal energy, standard and staggered magnetization, and the position and nature of the critical line, which confirm the mean-field qualitative picture, and which should be quantitatively reliable, at least in the high-temperature regime, including the entire critical line.

  16. Performance of synthetic antiferromagnetic racetrack memory: domain wall versus skyrmion

    KAUST Repository

    Tomasello, R

    2017-06-20

    A storage scheme based on racetrack memory, where the information can be coded in a domain or a skyrmion, seems to be an alternative to conventional hard disk drive for high density storage. Here, we perform a full micromagnetic study of the performance of synthetic antiferromagnetic (SAF) racetrack memory in terms of velocity and sensitivity to defects by using experimental parameters. We find that, to stabilize a SAF skyrmion, the Dzyaloshinskii–Moriya interaction in the top and the bottom ferromagnet should have an opposite sign. The velocity of SAF skyrmions and SAF Néel domain walls are of the same order and can reach values larger than 1200 m s−1 if a spin–orbit torque from the spin-Hall effect with opposite sign is applied to both ferromagnets. The presence of disordered anisotropy in the form of randomly distributed grains introduces a threshold current for both SAF skyrmions and SAF domain walls motions.

  17. Magnetocaloric properties of a frustrated Blume-Capel antiferromagnet

    Directory of Open Access Journals (Sweden)

    Žukovič Milan

    2014-07-01

    Full Text Available Low-temperature magnetization processes and magnetocaloric properties of a geometrically frustrated spin-1 Blume-Capel model on a triangular lattice are studied by Monte Carlo simulations. The model is found to display qualitatively different behavior depending on the sign of the single-ion anisotropy D. For positive values of D we observe two magnetization plateaus, similar to the spin-1/2 Ising antiferromagnet, and negative isothermal entropy changes for any field intensity. For a range of small negative values of D there are four magnetization plateaus and the entropy changes can be either negative or positive, depending on the field. If D is negative but large in absolute value then the entropy changes are solely positive.

  18. Producing coherent excitations in pumped Mott antiferromagnetic insulators

    Science.gov (United States)

    Wang, Yao; Claassen, Martin; Moritz, B.; Devereaux, T. P.

    2017-12-01

    Nonequilibrium dynamics in correlated materials has attracted attention due to the possibility of characterizing, tuning, and creating complex ordered states. To understand the photoinduced microscopic dynamics, especially the linkage under realistic pump conditions between transient states and remnant elementary excitations, we performed nonperturbative simulations of various time-resolved spectroscopies. We used the Mott antiferromagnetic insulator as a model platform. The transient dynamics of multiparticle excitations can be attributed to the interplay between Floquet virtual states and a modification of the density of states, in which interactions induce a spectral weight transfer. Using an autocorrelation of the time-dependent spectral function, we show that resonance of the virtual states with the upper Hubbard band in the Mott insulator provides the route towards manipulating the electronic distribution and modifying charge and spin excitations. Our results link transient dynamics to the nature of many-body excitations and provide an opportunity to design nonequilibrium states of matter via tuned laser pulses.

  19. Radiation enhanced antiferromagnetic exchange between spins in a superconducting host

    Science.gov (United States)

    Akkaravarawong, Kamphol; Vayrynen, Jukka; Sau, Jay; Glazman, Leonid; Yao, Norman

    2017-04-01

    A magnetic impurity on a conventional superconductor can host a localized bound state whose energy lies inside the superconducting gap. If the distance between two such impurities is smaller than the coherence length, the presence of these so-called Yu-Shiba-Rusinov (YSR) bound states can induce an antiferromagnetic exchange interaction between the impurities, falling off as 1 /r2 . Although the YSR interaction exhibits a slower decay than conventional RKKY interactions, its strength is significantly weaker, making it extremely challenging to experimentally observe. We demonstrate that the strength of the YSR interaction can be enhanced via radiation assisted virtual occupation, and that the signature of this coupling can naturally be observed through spectroscopy.

  20. Metamagnetic phase transition of the antiferromagnetic Heisenberg icosahedron.

    Science.gov (United States)

    Schröder, Christian; Schmidt, Heinz-Jürgen; Schnack, Jürgen; Luban, Marshall

    2005-05-27

    The observation of hysteresis effects in single molecule magnets like Mn12-acetate has initiated ideas of future applications in storage technology. The appearance of a hysteresis loop in such compounds is an outcome of their magnetic anisotropy. In this Letter we report that magnetic hysteresis occurs in a spin system without any anisotropy, specifically where spins mounted on the vertices of an icosahedron are coupled by antiferromagnetic isotropic nearest-neighbor Heisenberg interaction giving rise to geometric frustration. At T = 0 this system undergoes a first-order metamagnetic phase transition at a critical field Bc between two distinct families of ground state configurations. The metastable phase of the system is characterized by a temperature and field dependent survival probability distribution.

  1. Two Dimensional Antiferromagnetic Chern Insulator: NiRuCl6.

    Science.gov (United States)

    Zhou, P; Sun, C Q; Sun, L Z

    2016-10-12

    Density functional theory (DFT) and Berry curvature calculations show that quantum anomalous Hall effect (QAHE) can be realized in two-dimensional(2D) antiferromagnetic (AFM) NiRuCl6. The results indicate that NiRuCl6 behaves as an AFM Chern insulator and its spin-polarized electronic structure and strong spin-orbit coupling (SOC) are responsible for the QAHE. By tuning SOC, we found that the topological property of NiRuCl6 arises from its energy band inversion. Considering the compatibility between the AFM and insulators, AFM Chern insulator provides a new way to archive high temperature QAHE in experiments due to its different magnetic coupling mechanism from that of ferromagnetic (FM) Chern insulator.

  2. Alcohol increases hypnotic susceptibility.

    Science.gov (United States)

    Semmens-Wheeler, Rebecca; Dienes, Zoltán; Duka, Theodora

    2013-09-01

    One approach to hypnosis suggests that for hypnotic experience to occur frontal lobe activity must be attenuated. For example, cold control theory posits that a lack of awareness of intentions is responsible for the experience of involuntariness and/or the subjective reality of hypnotic suggestions. The mid-dorso-lateral prefrontal cortex and the ACC are candidate regions for such awareness. Alcohol impairs frontal lobe executive function. This study examined whether alcohol affects hypnotisability. We administered 0.8 mg/kg of alcohol or a placebo to 32 medium susceptible participants. They were subsequently hypnotised and given hypnotic suggestions. All participants believed they had received some alcohol. Participants in the alcohol condition were more susceptible to hypnotic suggestions than participants in the placebo condition. Impaired frontal lobe activity facilitates hypnotic responding, which supports theories postulating that attenuation of executive function facilitates hypnotic response, and contradicts theories postulating that hypnotic response involves enhanced inhibitory, attentional or other executive function. Copyright © 2013. Published by Elsevier Inc.

  3. Imaging Current-Induced Switching of Antiferromagnetic Domains in CuMnAs

    Science.gov (United States)

    Grzybowski, M. J.; Wadley, P.; Edmonds, K. W.; Beardsley, R.; Hills, V.; Campion, R. P.; Gallagher, B. L.; Chauhan, J. S.; Novak, V.; Jungwirth, T.; Maccherozzi, F.; Dhesi, S. S.

    2017-02-01

    The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using x-ray magnetic linear dichroism microscopy, we show that staggered effective fields generated by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multidomain antiferromagnetic films.

  4. Instability of paramagnetic state toward glassy state in random Ising antiferromagnet on tetrahedron cactus lattices

    Science.gov (United States)

    Yokota, Terufumi

    2018-01-01

    Ising antiferromagnet on tetrahedron cactus lattices with randomness in the exchange interactions is studied. Instability line of the paramagnetic state, beyond which glassy or antiferromagnetic state is (meta)stable is obtained. The model is investigated by the replica method. Instability toward antiferromagnetic state does not occur for M ≤ 4 where M is the number of corner sharing tetrahedra for the cactus lattices. Instability toward glassy state occurs at as weak randomness as J /(-J0) ≃ 0 . 056 , 0 . 020, and ≤ 10-4 for M = 2 , 3, and 4, respectively, where J0 and J2 are the mean and variance of the Gaussian random exchange interaction, respectively.

  5. Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism

    Science.gov (United States)

    Thielemann-Kühn, Nele; Schick, Daniel; Pontius, Niko; Trabant, Christoph; Mitzner, Rolf; Holldack, Karsten; Zabel, Hartmut; Föhlisch, Alexander; Schüßler-Langeheine, Christian

    2017-11-01

    By comparing femtosecond laser pulse induced ferro- and antiferromagnetic dynamics in one and the same material—metallic dysprosium—we show both to behave fundamentally different. Antiferromagnetic order is considerably faster and much more efficiently reduced by optical excitation than its ferromagnetic counterpart. We assign the fast and extremely efficient process in the antiferromagnet to an interatomic transfer of angular momentum within the spin system. Our findings imply that this angular momentum transfer channel is effective in other magnetic metals with nonparallel spin alignment. They also point out a possible route towards energy-efficient spin manipulation for magnetic devices.

  6. The spin-half XXZ antiferromagnet on the square lattice revisited: A high-order coupled cluster treatment

    Science.gov (United States)

    Bishop, R. F.; Li, P. H. Y.; Zinke, R.; Darradi, R.; Richter, J.; Farnell, D. J. J.; Schulenburg, J.

    2017-04-01

    We use the coupled cluster method (CCM) to study the ground-state properties and lowest-lying triplet excited state of the spin-half XXZ antiferromagnet on the square lattice. The CCM is applied to it to high orders of approximation by using an efficient computer code that has been written by us and which has been implemented to run on massively parallelized computer platforms. We are able therefore to present precise data for the basic quantities of this model over a wide range of values for the anisotropy parameter Δ in the range - 1 ≤ Δ 1) regimes, where Δ → ∞ represents the Ising limit. We present results for the ground-state energy, the sublattice magnetization, the zero-field transverse magnetic susceptibility, the spin stiffness, and the triplet spin gap. Our results provide a useful yardstick against which other approximate methods and/or experimental studies of relevant antiferromagnetic square-lattice compounds may now compare their own results. We also focus particular attention on the behaviour of these parameters for the easy-axis system in the vicinity of the isotropic Heisenberg point (Δ = 1) , where the model undergoes a phase transition from a gapped state (for Δ > 1) to a gapless state (for Δ ≤ 1), and compare our results there with those from spin-wave theory (SWT). Interestingly, the nature of the criticality at Δ = 1 for the present model with spins of spin quantum number s =1/2 that is revealed by our CCM results seems to differ qualitatively from that predicted by SWT, which becomes exact only for its near-classical large-s counterpart.

  7. Dynamic magnetic susceptibility of systems with long-range magnetic order

    Energy Technology Data Exchange (ETDEWEB)

    Vannette, Matthew Dano [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    The utility of the TDR as an instrument in the study of magnetically ordered materials has been expanded beyond the simple demonstration purposes. Results of static applied magnetic field dependent measurements of the dynamic magnetic susceptibility, χ, of various ferromagnetic (FM) and antiferromagnetic (AFM) materials showing a range of transition temperatures (1-800 K) are presented. Data was collected primarily with a tunnel diode resonator (TDR) at different radio-frequencies (~10-30 MHz). In the vicinity of TC local moment ferromagnets show a very sharp, narrow peak in χ which is suppressed in amplitude and shifted to higher temperatures as the static bias field is increased. Unexpectedly, critical scaling analysis fails for these data. It is seen that these data are frequency dependent, however there is no simple method whereby measurement frequency can be changed in a controllable fashion. In contrast, itinerant ferromagnets show a broad maximum in χ well below TC which is suppressed and shifts to lower temperatures as the dc bias field is increased. The data on itinerant ferromagnets is fitted to a semi-phenomenological model that suggests the sample response is dominated by the uncompensated minority spins in the conduction band. Concluding remarks suggest possible scenarios to achieve frequency resolved data using the TDR as well as other fields in which the apparatus may be exploited.

  8. Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases

    Energy Technology Data Exchange (ETDEWEB)

    Gottwald, Tobias

    2010-08-27

    In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe

  9. Antiferromagnetism in metals: from the cuprate superconductors to the heavy fermion materials.

    Science.gov (United States)

    Sachdev, Subir; Metlitski, Max A; Punk, Matthias

    2012-07-25

    The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near this critical point is reviewed: it involves a subtle interplay between the breakdown of fermionic quasiparticle excitations on the Fermi surface and the strong pairing glue provided by the antiferromagnetic fluctuations. The net result is a logarithm-squared enhancement of the pairing vertex for generic Fermi surfaces, with a universal dimensionless coefficient independent of the strength of interactions, which is expected to lead to superconductivity at the scale of the Fermi energy. We also discuss the possibility that the antiferromagnetic critical point can be replaced by an intermediate 'fractionalized Fermi liquid' phase, in which there is Fermi surface reconstruction but no long-range antiferromagnetic order. We discuss the relevance of this phase to the underdoped cuprates and the heavy fermion materials.

  10. Theoretical Analysis of Inertia-like Switching in Magnets: Applications to a Synthetic Antiferromagnet

    National Research Council Canada - National Science Library

    Bhattacharjee, Satadeep; Bergman, Anders; Taroni, Andrea; Hellsvik, Johan; Sanyal, Biplab; Eriksson, Olle

    2012-01-01

    The magnetization dynamics of a synthetic antiferromagnet subjected to a short-magnetic-field pulse has been studied by using a combination of first principles calculations and atomistic spin-dynamics simulations...

  11. Spin waves treatment of the antiferromagnetic ground state of two Ising-like systems

    Directory of Open Access Journals (Sweden)

    Adegoke Kunle

    2014-01-01

    Full Text Available Using Anderson's spin wave theory, we derive expressions for the ground state energy of two Ising-like systems. Antiferromagnetic long range order is predicted for one of the systems.

  12. Ground state configurations in antiferromagnetic ultrathin films with dipolar anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Leon, H., E-mail: hleon@imre.oc.uh.cu [Instituto de Ciencia y Tecnologia de Materiales, Universidad de La Habana, Zapata e/ Mazon y G. Vedado, 10400 La Habana (Cuba)

    2013-02-15

    The formalism developed in a previous work to calculate the dipolar energy in quasi-two-dimensional crystals with ferromagnetic order is now extended to collinear antiferromagnetic order. Numerical calculations of the dipolar energy are carried out for systems with tetragonally distorted fcc [001] structures, the case of NiO and MnO ultrathin film grown in non-magnetic substrates, where the magnetic phase is a consequence of superexchange and dipolar interactions. The employed approximation allows to demonstrate that dipolar coupling between atomic layers is responsible for the orientation of the magnetization when it differs from the one in a single layer. The ground state energy of a given NiO or MnO film is found to depend not only on the strain, but also on how much the interlayer separation and the 2D lattice constant are changed with respect to the ideal values corresponding to the non-distorted cubic structure. Nevertheless, it is shown that the orientation of the magnetization in the magnetic phase of any of these films is determined by the strain exclusively. A striped phase with the magnetization along the [112{sup Macron }] direction appears as the ground state configuration of NiO and MnO ultrathin films. In films with equally oriented stripes along the layers this magnetic phase is twofold degenerate, while in films with multidomain layers it is eightfold degenerate. These results are not in contradiction with experimentally observed out-of-plane or in-plane magnetization of striped phases in NiO and MnO ultrathin films. - Highlights: Black-Right-Pointing-Pointer Dipolar energy in collinear antiferromagnetic ultrathin films is calculated. Black-Right-Pointing-Pointer Numerical results are presented for distorted fcc [001] structures. Black-Right-Pointing-Pointer The lowest energy of a system depends on how the tetragonal distortion is achieved. Black-Right-Pointing-Pointer A striped phase with magnetization in the [112{sup Macron }] direction is the

  13. Relaxation of antiferromagnetic order in spin-1/2 chains following a quantum quench.

    Science.gov (United States)

    Barmettler, Peter; Punk, Matthias; Gritsev, Vladimir; Demler, Eugene; Altman, Ehud

    2009-04-03

    We study the unitary time evolution of antiferromagnetic order in anisotropic Heisenberg chains that are initially prepared in a pure quantum state far from equilibrium. Our analysis indicates that the antiferromagnetic order imprinted in the initial state vanishes exponentially. Depending on the anisotropy parameter, oscillatory or nonoscillatory relaxation dynamics is observed. Furthermore, the corresponding relaxation time exhibits a minimum at the critical point, in contrast to the usual notion of critical slowing down, from which a maximum is expected.

  14. Spin Dynamics and Critical Fluctuations in a Two-Dimensional Random Antiferromagnet

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.

    1975-01-01

    A comprehensive elastic- and inelastic-neutron-scattering study of the binary mixed antiferromagnet Rb2Mn0.5Ni0.5F4 has been carried out. The pure materials, Rb2MnF4 and Rb2NiF4 are [2d] near-Heisenberg antiferromagnets of the K2NiF4 type. Elastic-scattering experiments demonstrate that the Mn...

  15. One- and Two- Magnon Excitations in a One-Dimensional Antiferromagnet in a Magnetic Field

    DEFF Research Database (Denmark)

    Heilmann, I.U.; Kjems, Jørgen; Endoh, Y.

    1981-01-01

    We have carried out a comprehensive experimental and theoretical study of the inelastic scattering in the one-dimensional near-Heisenberg antiferromagnet (CD3)4NMnCl3 (TMMC) at low temperatures, 0.3......We have carried out a comprehensive experimental and theoretical study of the inelastic scattering in the one-dimensional near-Heisenberg antiferromagnet (CD3)4NMnCl3 (TMMC) at low temperatures, 0.3...

  16. Multicritical points in the three-dimensional XXZ antiferromagnet with single-ion anisotropy.

    Science.gov (United States)

    Selke, Walter

    2013-01-01

    The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy, the XXZ model, and competing planar single-ion anisotropy in a magnetic field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. The biconical (supersolid) phase, bordering the antiferromagnetic and spin-flop phases, is found to become thermally unstable well below the onset of the disordered, paramagnetic phase, leading to interesting multicritical points.

  17. Spin-density-wave antiferromagnetism of Cr in Fe/Cr(001) superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Fullerton, E.E.; Bader, S.D. [Argonne National Lab., IL (United States); Robertson, J.L. [Oak Ridge National Lab., TN (United States)

    1996-10-01

    The antiferromagnetic spin-density-wave (SDW) order of Cr layers in Fe/Cr(001) superlattices was investigated by neutron scattering. For Cr thickness 51-190 {Angstrom}, a transverse SDW is formed for all temperatures below Neel temperature with a single wavevector Q normal to the layers. A coherent magnetic structure forms with the nodes of the SDW near the Fe-Cr interfaces. For thinner Cr layers, the magnetic scattering can be described by commensurate antiferromagnetic order.

  18. Structural Distortion Stabilizing the Antiferromagnetic and Semiconducting Ground State of BaMn2As2

    Directory of Open Access Journals (Sweden)

    Ekkehard Krüger

    2016-09-01

    Full Text Available We report evidence that the experimentally found antiferromagnetic structure as well as the semiconducting ground state of BaMn 2 As 2 are caused by optimally-localized Wannier states of special symmetry existing at the Fermi level of BaMn 2 As 2 . In addition, we find that a (small tetragonal distortion of the crystal is required to stabilize the antiferromagnetic semiconducting state. To our knowledge, this distortion has not yet been established experimentally.

  19. Nematic ordering in pyrochlore antiferromagnets: high-field phase of chromium spinel oxides

    OpenAIRE

    Takata, Emika; Momoi, Tsutomu; Oshikawa, Masaki

    2015-01-01

    Motivated by recent observation of a new high field phase near saturation in chromium spinels $A$Cr$_2$O$_4$ ($A=$ Zn, Cd, Hg), we study the $S = 3/2$ pyrochlore Heisenberg antiferromagnet with biquadratic interactions. Magnon instability analysis at the saturation field reveals that a very small biquadratic interaction can induce magnon pairing in pyrochlore antiferromagnets, which leads to the emergence of a ferro-quadrupolar phase, or equivalently a spin nematic phase, below the saturation...

  20. Zero Modes and Global Antiferromagnetism in Strained Graphene

    Directory of Open Access Journals (Sweden)

    Bitan Roy

    2014-05-01

    Full Text Available A novel magnetic ground state is reported for the Hubbard Hamiltonian in strained graphene. When the chemical potential lies close to the Dirac point, the ground state exhibits locally both the Néel and ferromagnetic orders, even for weak Hubbard interaction. Whereas the Néel order parameter remains of the same sign in the entire system, the magnetization at the boundary takes the opposite sign from the bulk. The total magnetization vanishes this way, and the magnetic ground state is globally only an antiferromagnet. This peculiar ordering stems from the nature of the strain-induced single-particle zero-energy states, which have support on one sublattice of the honeycomb lattice in the bulk, and on the other sublattice near the boundary of a finite system. We support our claim with the self-consistent numerical calculation of the order parameters, as well as by the Monte Carlo simulations of the Hubbard model in both uniformly and nonuniformly strained honeycomb lattice. The present result is contrasted with the magnetic ground state of the same Hubbard model in the presence of a true magnetic field (and for vanishing Zeeman coupling, which is exclusively Néel ordered, with zero local magnetization everywhere in the system.

  1. Cluster multipole theory for anomalous Hall effect in antiferromagnets

    Science.gov (United States)

    Suzuki, M.-T.; Koretsune, T.; Ochi, M.; Arita, R.

    2017-03-01

    We introduce a cluster extension of multipole moments to discuss the anomalous Hall effect (AHE) in both ferromagnetic (FM) and antiferromagnetic (AFM) states in a unified framework. We first derive general symmetry requirements for the AHE in the presence or absence of the spin-orbit coupling by considering the symmetry of the Berry curvature in k space. The cluster multipole (CMP) moments are then defined to quantify the macroscopic magnetization in noncollinear AFM states as a natural generalization of the magnetization in FM states. We identify the macroscopic CMP order which induces the AHE. The theoretical framework is applied to the noncollinear AFM states of Mn3Ir , for which an AHE was predicted in a first-principles calculation, and Mn3Z (Z =Sn ,Ge ), for which a large AHE was recently discovered experimentally. We further compare the AHE in Mn3Z and bcc Fe in terms of the CMP. We show that the AHE in Mn3Z is characterized by the magnetization of a cluster octupole moment in the same manner as that in bcc Fe characterized by the magnetization of the dipole moment.

  2. Spintronic materials and devices based on antiferromagnetic metals

    Directory of Open Access Journals (Sweden)

    Y.Y. Wang

    2017-04-01

    Full Text Available In this paper, we review our recent experimental developments on antiferromagnet (AFM spintronics mainly comprising Mn-based noncollinear AFM metals. IrMn-based tunnel junctions and Hall devices have been investigated to explore the manipulation of AFM moments by magnetic fields, ferromagnetic materials and electric fields. Room-temperature tunneling anisotropic magnetoresistance based on IrMn as well as FeMn has been successfully achieved, and electrical control of the AFM exchange spring is realized by adopting ionic liquid. In addition, promising spin-orbit effects in AFM as well as spin transfer via AFM spin waves reported by different groups have also been reviewed, indicating that the AFM can serve as an efficient spin current source. To explore the crucial role of AFM acting as efficient generators, transmitters, and detectors of spin currents is an emerging topic in the field of magnetism today. AFM metals are now ready to join the rapidly developing fields of basic and applied spintronics, enriching this area of solid-state physics and microelectronics.

  3. Observation of Ultrafast Magnon Dynamics in Antiferromagnetic Nickel Oxide by Optical Pump-Probe and Terahertz Time-Domain Spectroscopies

    Science.gov (United States)

    Kohmoto, T.; Moriyasu, T.; Wakabayashi, S.; Jinn, H.; Takahara, M.; Kakita, K.

    2018-01-01

    We have studied the ultrafast magnon dynamics in an antiferromagnetic 3d-transition-metal monoxide, nickel oxide (NiO), using optical pump-probe spectroscopy and terahertz time-domain spectroscopy (THz-TDS). THz damped magnon oscillations were observed in the Faraday rotation signal and in the transmitted THz electric field via optical pump-probe spectroscopy and THz-TDS, respectively. The magnon signals were observed in both the optical pump-probe spectroscopy and THz-TDS experiments, which shows that both Raman- and infrared-active modes are included in the NiO magnon modes. The magnon relaxation rate observed using THz-TDS was found to be almost constant up to the Néel temperature T N (= 523 K) and to increase abruptly near that temperature. This shows that temperature-independent spin-spin relaxation dominates up to T N . In our experiment, softening of the magnon frequency near T N was clearly observed. This result shows that the optical pump-probe spectroscopy and THz-TDS have high frequency resolution and a high signal to noise ratio in the THz region. We discuss the observed temperature dependence of the magnon frequencies using three different molecular field theories. The experimental results suggest that the biquadratic contribution of the exchange interaction plays an important role in the temperature dependence of the sublattice magnetization and the magnon frequency in cubic antiferromagnetic oxides.

  4. Observation of Ultrafast Magnon Dynamics in Antiferromagnetic Nickel Oxide by Optical Pump-Probe and Terahertz Time-Domain Spectroscopies

    Science.gov (United States)

    Kohmoto, T.; Moriyasu, T.; Wakabayashi, S.; Jinn, H.; Takahara, M.; Kakita, K.

    2017-09-01

    We have studied the ultrafast magnon dynamics in an antiferromagnetic 3d-transition-metal monoxide, nickel oxide (NiO), using optical pump-probe spectroscopy and terahertz time-domain spectroscopy (THz-TDS). THz damped magnon oscillations were observed in the Faraday rotation signal and in the transmitted THz electric field via optical pump-probe spectroscopy and THz-TDS, respectively. The magnon signals were observed in both the optical pump-probe spectroscopy and THz-TDS experiments, which shows that both Raman- and infrared-active modes are included in the NiO magnon modes. The magnon relaxation rate observed using THz-TDS was found to be almost constant up to the Néel temperature T N (= 523 K) and to increase abruptly near that temperature. This shows that temperature-independent spin-spin relaxation dominates up to T N . In our experiment, softening of the magnon frequency near T N was clearly observed. This result shows that the optical pump-probe spectroscopy and THz-TDS have high frequency resolution and a high signal to noise ratio in the THz region. We discuss the observed temperature dependence of the magnon frequencies using three different molecular field theories. The experimental results suggest that the biquadratic contribution of the exchange interaction plays an important role in the temperature dependence of the sublattice magnetization and the magnon frequency in cubic antiferromagnetic oxides.

  5. Evolution of spin excitations in a gapped antiferromagnet from the quantum to the high-temperature limit

    DEFF Research Database (Denmark)

    Kenzelmann, M.; Cowley, R.A.; Buyers, W.J.L.

    2002-01-01

    We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar o...... and the experiment is not consistent with the random phase approximation for coupled quantum chains. At T=200 K, the structure factor and second energy moment of the excitation spectrum are in excellent agreement with the high-temperature series expansion.......We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar...... is in agreement with quantum Monte Carlo calculations for the spin-1 chain. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12 K where three-dimensional spin correlations are important, xi is shorter than predicted...

  6. Antiferromagnetic spintronics of Mn{sub 2}Au: An experiment, first principle, mean field and series expansions calculations study

    Energy Technology Data Exchange (ETDEWEB)

    Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63 46000, Safi (Morocco); LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble Cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Boutahar, A.; Lassri, H. [LPMMAT, Université Hassan II-Casablanca, Faculté des Sciences, BP 5366 Maârif (Morocco)

    2015-11-01

    The self-consistent ab initio calculations, based on DFT (Density Functional Theory) approach and using FLAPW (Full potential Linear Augmented Plane Wave) method, are performed to investigate both electronic and magnetic properties of the Mn{sub 2}Au. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Mn plans. Magnetic moment considered to lie along (110) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn–Mn in Mn{sub 2}Au are given by using the experiment results and the mean field theory. The High Temperature Series Expansions (HTSEs) of the magnetic susceptibility with the magnetic moments in Mn{sub 2}Au (m{sub Mn}) is given up to tenth order series in, 1/k{sub B}T. The Néel temperature T{sub N} is obtained by HTSEs combined with the Padé approximant method. The critical exponent associated with the magnetic susceptibility is deduced as well. - Highlights: • The both electronic and magnetic properties of the Mn{sub 2}Au are studied. • The exchange interactions between the magnetic atoms Mn–Mn in Mn{sub 2}Au are given. • The Néel temperature T{sub N} of Mn{sub 2}Au is obtained by HTSEs method. • The critical exponent associated with the magnetic susceptibility is deduced.

  7. Sequential structural and antiferromagnetic transitions in BaFe2Se3 under pressure

    Science.gov (United States)

    Zhang, Yang; Lin, Ling-Fang; Zhang, Jun-Jie; Dagotto, Elbio; Dong, Shuai

    2018-01-01

    The discovery of superconductivity in the two-leg ladder compound BaFe2S3 has established the 123-type iron chalcogenides as a novel and interesting subgroup of the iron-based superconductor family. However, in this 123 series, BaFe2Se3 is an exceptional member, with a magnetic order and crystalline structure different from all others. Recently, an exciting experiment reported the emergence of superconductivity in BaFe2Se3 at high pressure [J. Ying et al., Phys. Rev. B 95, 241109(R) (2017), 10.1103/PhysRevB.95.241109]. In this paper, we report a first-principles study of BaFe2Se3 . Our analysis unveils a variety of qualitative differences between BaFe2S3 and BaFe2Se3 , including in the latter an unexpected chain of transitions with increasing pressure. First, by gradually reducing the tilting angle of iron ladders, the crystalline structure smoothly transforms from P n m a to C m c m at ˜6 GPa. Second, the system becomes metallic at 10.4 GPa. Third, its unique ambient-pressure Block antiferromagnetic ground state is replaced by the more common stripe (so-called CX-type) antiferromagnetic order at ˜12 GPa, the same magnetic state as the 123-S ladder. This transition is found at a pressure very similar to the experimental superconducting transition. Finally, all magnetic moments vanish at 30 GPa. This reported theoretical diagram of the complete phase evolution is important because of the technical challenges to capture many physical properties in high-pressure experiments. The information obtained in our calculations suggests different characteristics for superconductivity in BaFe2Se3 and BaFe2S3 : in 123-S pairing occurs when magnetic moments vanish, while in 123-Se the transition region from Block- to CX-type magnetism appears to catalyze superconductivity. Finally, an additional superconducting dome above ˜30 GPa is expected to occur.

  8. Antiferromagnetic CsCrF{sub 5} and canted antiferromagnetism in RbCrF{sub 5} and KCrF{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Jagličić, Zvonko, E-mail: zvonko.jaglicic@imfm.si [University of Ljubljana, Faculty of Civil and Geodetic Engineering, and Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana (Slovenia); Mazej, Zoran, E-mail: zoran.mazej@ijs.si [Department of Inorganic Chemistry and Technology, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia)

    2017-07-15

    Highlights: • Cr(IV) ions are antiferromagnetically coupled within chains in ACrF{sub 5} (A = Cs, Rb, K). • Small structural difference causes huge difference in magnetic properties below 10 K. • Canted antiferromagnetism has been observed in RbCrF{sub 5} and KCrF{sub 5} at low temperature. - Abstract: In ACrF{sub 5} (A = Cs, Rb, K), Cr(IV) ions are coordinated by six fluoride ligands where the resulting CrF{sub 6} octahedra share cis vertexes to form infinite chains of ([Cr{sup IV}F{sub 5}]{sup −}){sub n}. The geometry of the latter in Cs compound differs from that in K and Rb compounds. The results of investigations of the magnetic behaviour of these compounds have shown that an antiferromagnetic superexchange interaction is present within the chains with J{sub Cs} = −10.2 cm{sup −1}, J{sub Rb} = −13.3 cm{sup −1}, and J{sub K} = −13.1 cm{sup −1}. Additional ferromagnetic-like long-range ordering has been observed in KCrF{sub 5} and RbCrF{sub 5} below 6 K which can be explained, in a correlation with their crystal structures, as canted antiferromagnetism.

  9. Design of L2_1-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT+GW study

    OpenAIRE

    Tas, M.; Sasioglu, E.; Friedrich, C.; Blugel, S.; Galanakis, I.

    2016-01-01

    Antiferromagnetic spintronics is an on-going growing field of research. Employing both standard density functional theory and the $GW$ approximation within the framework of the FLAPW method, we study the electronic and magnetic properties of seven potential antiferromagnetic semiconducting Heusler compounds with 18 (or 28 when Zn is present) valence electrons per unit cell. We show that in these compounds G-type antiferromagnetism is the ground state and that they are all either emiconductors...

  10. Dominant ferromagnetic coupling over antiferromagnetic in Ni doped ZnO: First-principles calculations

    Science.gov (United States)

    Haq, Bakhtiar Ul; Ahmed, Rashid; Abdellatif, Galila; Shaari, Amiruddin; Butt, Faheem K.; Kanoun, Mohammed Benali; Goumri-Said, Souraya

    2016-02-01

    The low magnetic moment (MM) in diluted magnetic semiconductors (DMS) at low impurity doping levels has triggered considerable research into condensed magnetic semiconductors (CMS).This work reports an ab-initio investigation of the electronic structures and magnetic properties of ZnO in a zinc-blende (ZB) structure doped with nickel ions. Ni-doped ZnO-based DMS and CMS exhibit a dominance of ferromagnetic coupling over antiferromagnetic. A robust increase in the magnetization has been observed as a function of Ni impurity levels. This material favors short-range magnetic interactions at the ground state, suggesting that the observed ferromagnetism is defined by the double exchange mechanism. The spin-polarized density of states (DOS) of Ni-doped ZnO characterizes it as half-metallic with a considerable energy gap for up-spin components and as metallic for-down spins. Half-metallic Ni:ZnO based magnetic semiconductors with high magnetization are expected to have potential applications in spintronics.

  11. Spin-glass and antiferromagnetic transitions in Ru2-xFexCrSi

    Science.gov (United States)

    Hiroi, Masahiko; Ko, Haku; Nakashima, Shingo; Shigeta, Iduru; Ito, Masakazu; Manaka, Hirotaka; Terada, Norio

    2012-12-01

    In this study the properties of the Heusler compounds Ru2-xFexCrSi (0CrSi was revealed to exhibit two anomalies in the temperature dependence of magnetization M(T); one is a peak in M(T) at T*N ~ 30 K and the other is strong irreversibility in M(T) below T*N, the onset of which is defined as Tg. M(T) and specific heat CP(T) of Ru2CrSi are measured. A clear peak is observed in both M(T) and CP(T). This is in quite contrast to the case for Ru1.9Fe0.1CrSi, where no anomaly in CP(T) was observed at T*N or at any other temperatures. These indicate that an antiferromagnetic transition occurs at TN = 14 K in Ru2CrSi. For x = 0.02 the characteristic two anomalies in M(T) are also found at various magnetic fields, and their field dependence is basically the same as that for x = 0.1. These two anomalies are suggestive of successive spin-glass transitions. As for the dependence of the two anomalies on x, Tg does not change with x, whereas T*N decreases with decreasing x and seems to approach Tg at zero field.

  12. Structural and magnetic properties in Heusler-type ferromagnet/antiferromagnet bilayers

    Science.gov (United States)

    Fukatani, N.; Inagaki, K.; Miyawaki, T.; Ueda, K.; Asano, H.

    2013-05-01

    The structure and magnetic properties of Heusler ferromagnet/antiferromagnet (FM/AFM) bilayers were investigated. Structural characterization revealed that Fe2CrSi/Ru2MnGe bilayers were epitaxially grown with an L21 ordered structure when the Ru2MnGe growth temperature was 573 K. The magnetization curve indicates that exchange bias occurs in the Fe2CrSi/Ru2MnGe bilayers at 77 K. The appearance of an exchange-anisotropy field Hex depends on the growth of Ru2MnGe layer, indicating that the exchange bias originates from the epitaxial Fe2CrSi/Ru2MnGe interface. The exchange anisotropy energy Jk of the Fe2CrSi/Ru2MnGe and Co2MnGe/Ru2MnGe bilayer systems appears to follow a Heisenberg-like exchange coupling model. This suggests that the Cr and Mn interface atoms in the FM layers play significant roles in exchange coupling in the Fe2CrSi/Ru2MnGe and Co2MnGe/Ru2MnGe bilayer systems, respectively.

  13. Pressure induced superconductivity in the antiferromagnetic Dirac material BaMnBi2.

    Science.gov (United States)

    Chen, Huimin; Li, Lin; Zhu, Qinqing; Yang, Jinhu; Chen, Bin; Mao, Qianhui; Du, Jianhua; Wang, Hangdong; Fang, Minghu

    2017-05-09

    The so-called Dirac materials such as graphene and topological insulators are a new class of matter different from conventional metals and (doped) semiconductors. Superconductivity induced by doing or applying pressure in these systems may be unconventional, or host mysterious Majorana fermions. Here, we report a successfully observation of pressure-induced superconductivity in an antiferromagnetic Dirac material BaMnBi2 with T c of ~4 K at 2.6 GPa. Both the higher upper critical field, μ 0 H c2(0) ~ 7 Tesla, and the measured current independent of T c precludes that superconductivity is ascribed to the Bi impurity. The similarity in ρ ab (B) linear behavior at high magnetic fields measured at 2 K both at ambient pressure (non-superconductivity) and 2.6 GPa (superconductivity, but at the normal state), as well as the smooth and similar change of resistivity with pressure measured at 7 K and 300 K in zero field, suggests that there may be no structure transition occurred below 2.6 GPa, and superconductivity observed here may emerge in the same phase with Dirac fermions. Our findings imply that BaMnBi2 may provide another platform for studying SC mechanism in the system with Dirac fermions.

  14. Antiferromagnetic Dichroism in a Complex Multisublattice Magnetoelectric CuB(2)O(4).

    Science.gov (United States)

    Boldyrev, K N; Pisarev, R V; Bezmaternykh, L N; Popova, M N

    2015-06-19

    Magnetic control of the crystal chirality was announced by Saito et al. [Phys. Rev. Lett. 101, 117402 (2008)] on the ground of experiments in CuB(2)O(4). This claim has raised a sharp dispute in the literature because it seemed to contradict the fundamental symmetry principles. We settle this dispute on the basis of a high-resolution optical spectroscopy study of excitonic transitions in CuB(2)O(4). We find that a large sublattice-sensitive antiferromagnetic linear dichroism (LD) emerges at the Néel temperature T(N)=21  K and show how it could simulate a "magnetic-field control of the crystal chirality." We prove that the discovered LD is related microscopically to the magnetic Davydov splitting. This LD is highly sensitive to subtle changes in the spin subsystems, which allowed us to observe a splitting of the phase transition into an incommensurate magnetic phase into two transitions (T(1)(*)=8.5 and T(2)(*)=7.9  K) and to suggest elliptical spiral structures below T(1)(*), instead of a simple circular helix proposed earlier.

  15. New Insulating Antiferromagnetic Quaternary Iridates MLa10Ir4O24 (M = Sr, Ba)

    Science.gov (United States)

    Zhao, Qingbiao; Han, Fei; Stoumpos, Constantinos C.; Han, Tian-Heng; Li, Hao; Mitchell, J. F.

    2015-07-01

    Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4O24 is an insulator.

  16. Longitudinal optical and spin Hall conductivities of Rashba conducting strips coupled to ferromagnetic and antiferromagnetic layers

    Science.gov (United States)

    Riera, José A.

    2017-01-01

    A system composed of a conducting planar strip with Rashba spin-orbit coupling (RSOC), magnetically coupled to a layer of localized magnetic moments, at equilibrium, is studied within a microscopic Hamiltonian with numerical techniques at zero temperature in the clean limit. In particular, transport properties for the cases of ferromagnetic (FM) and antiferromagnetic (AFM) coupled layers are computed in linear response on strips of varying width. Some behaviors observed for these properties are consistent with the ones observed for the corresponding Rashba helical currents. The case of uncoupled Rashba strips is also studied for comparison. In the case of Rashba strips coupled to an AFM localized order, results for the longitudinal dc conductivity, for small strip widths, suggest the proximity to a metal-insulator transition. More interesting, in the proximity of this transition, and in general at intermediate values of the RSOC, a large spin Hall conductivity is observed that is two orders of magnitude larger than the one for the FM order for the same values of the RSOC and strip widths. There are clearly two different regimes for small and for large RSOC, which is also present in the behavior of Rashba helical currents. Different contributions to the optical and the spin Hall conductivities, according to a new classification of inter- or intraband origin proposed for planar strips in the clean limit, or coming from the hopping or spin-orbit terms of the Hamiltonian, are examined. Finally, the effects of different orientation of the coupled magnetic moments will be also studied.

  17. Sequences of ground states and classification of frustration in odd-numbered antiferromagnetic rings

    Science.gov (United States)

    Florek, Wojciech; Antkowiak, Michał; Kamieniarz, Grzegorz

    2016-12-01

    The sequences of ground states in frustrated antiferromagnetic rings with odd number of local spins characterized by a single bond defect or by arbitrary uniform couplings to an additional spin located at the center are determined. The sequences provide firm constraints on the total ground-state quantum numbers, which are more stringent than those arising from the Lieb-Mattis theorem for bipartite quantum spin systems. Apart from their theoretical importance, they suggest the possibility of tailoring a given class of the molecular nanomagnets with desired ground-state properties by tuning the relevant couplings. In particular, they predict the spin S =1 /2 ground state for the centered rings composed of the half-integer spins with approximately uniform interactions. They confirm the applicability of the recent classification of spin frustration in both types of molecular nanomagnets. The classification is also discussed in the classical limit for the first class of the rings, providing a direct picture of frustration types. The Lieb-Mattis energy-level ordering and an analog of the Landé band, i.e., the energy spectra properties simplifying the characterization of the rings using the bulk magnetic or NMR measurements, are briefly discussed.

  18. Large anomalous Nernst effect at room temperature in a chiral antiferromagnet

    Science.gov (United States)

    Ikhlas, Muhammad; Tomita, Takahiro; Koretsune, Takashi; Suzuki, Michi-To; Nishio-Hamane, Daisuke; Arita, Ryotaro; Otani, Yoshichika; Nakatsuji, Satoru

    2017-11-01

    A temperature gradient in a ferromagnetic conductor can generate a transverse voltage drop perpendicular to both the magnetization and heat current. This anomalous Nernst effect has been considered to be proportional to the magnetization, and thus observed only in ferromagnets. Theoretically, however, the anomalous Nernst effect provides a measure of the Berry curvature at the Fermi energy, and so may be seen in magnets with no net magnetization. Here, we report the observation of a large anomalous Nernst effect in the chiral antiferromagnet Mn 3Sn (ref. ). Despite a very small magnetization ~0.002 μB per Mn, the transverse Seebeck coefficient at zero magnetic field is ~0.35 μV K-1 at room temperature and reaches ~0.6 μV K-1 at 200 K, which is comparable to the maximum value known for a ferromagnetic metal. Our first-principles calculations reveal that this arises from a significantly enhanced Berry curvature associated with Weyl points near the Fermi energy. As this effect is geometrically convenient for thermoelectric power generation--it enables a lateral configuration of modules to cover a heat source--these observations suggest that a new class of thermoelectric materials could be developed that exploit topological magnets to fabricate efficient, densely integrated thermopiles.

  19. Pb2MnTeO6 Double Perovskite: An Antipolar Anti-ferromagnet.

    Science.gov (United States)

    Retuerto, Maria; Skiadopoulou, Stella; Li, Man-Rong; Abakumov, Artem M; Croft, Mark; Ignatov, Alexander; Sarkar, Tapati; Abbett, Brian M; Pokorný, Jan; Savinov, Maxim; Nuzhnyy, Dmitry; Prokleška, Jan; Abeykoon, Milinda; Stephens, Peter W; Hodges, Jason P; Vaněk, Přemysl; Fennie, Craig J; Rabe, Karin M; Kamba, Stanislav; Greenblatt, Martha

    2016-05-02

    Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ∼120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s(2) lone-pair electrons, together with a surprising off-centering of Mn(2+) (d(5)) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ∼150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6.

  20. Antiferromagnetic transitions of osmium-containing rare earth double perovskites Ba{sub 2}LnOsO{sub 6} (Ln=rare earths)

    Energy Technology Data Exchange (ETDEWEB)

    Hinatsu, Yukio, E-mail: hinatsu@sci.hokudai.ac.jp; Doi, Yoshihiro; Wakeshima, Makoto

    2013-10-15

    The perovskite-type compounds containing both rare earth and osmium Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm–Lu) have been prepared. Powder X-ray diffraction measurements and Rietveld analysis show that Ln{sup 3+} and Os{sup 5+} ions are structurally ordered at the M site of the perovskite BaMO{sub 3}. Magnetic susceptibility and specific heat measurements show that an antiferromagnetic ordering of Os{sup 5+} ions has been observed for Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm, Eu, Gd, Lu) at 65–71 K. Magnetic ordering of Ln{sup 3+} moments occurs when the temperature is furthermore decreased. - Graphical abstract: The perovskite-type compounds containing both rare earth and osmium Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm–Lu) have been prepared. An antiferromagnetic ordering of Os{sup 5+} ions has been observed for Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm, Eu, Gd, Lu) at 65–71 K. Measurements and analysis of the specific heat for Ba{sub 2}PrOsO{sub 6} show that magnetic ordering of the Pr{sup 3+} moments should have occurred at ∼20 K. Display Omitted.

  1. Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe

    Science.gov (United States)

    Kriegner, D.; Výborný, K.; Olejník, K.; Reichlová, H.; Novák, V.; Marti, X.; Gazquez, J.; Saidl, V.; Němec, P.; Volobuev, V. V.; Springholz, G.; Holý, V.; Jungwirth, T.

    2016-06-01

    Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II-VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Néel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets.

  2. Effect of antiferromagnetic interfacial coupling on spin-wave resonance frequency of multi-layer film

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Rong-ke, E-mail: rkqiu@163.com; Cai, Wei

    2017-08-15

    Highlights: • A quantum approach is developed to study the SWR of a bicomponent multi-layer films. • The comparison of the SWR in films with FM and AFM interfacial coupling has been made. • The present results show the method to enhance and adjust the SWR frequency of films. - Abstract: We investigate the spin-wave resonance (SWR) frequency in a bicomponent bilayer and triple-layer films with antiferromagnetic or ferromagnetic interfacial couplings, as function of interfacial coupling, surface anisotropy, interface anisotropy, thickness and external magnetic field, using the linear spin-wave approximation and Green’s function technique. The microwave properties for multi-layer magnetic film with antiferromagnetic interfacial coupling is different from those for multi-layer magnetic film with ferromagnetic interfacial coupling. For the bilayer film with antiferromagnetic interfacial couplings, as the lower (upper) surface anisotropy increases, only the SWR frequencies of the odd (even) number modes increase. The lower (upper) surface anisotropy does not affect the SWR frequencies of the even (odd) number modes{sub .} For the multi-layer film with antiferromagnetic interfacial coupling, the SWR frequency of modes m = 1, 3 and 4 decreases while that of mode m = 2 increases with increasing thickness of the film within a proper parameter region. The present results could be useful in enhancing our fundamental understanding and show the method to enhance and adjust the SWR frequency of bicomponent multi-layer magnetic films with antiferromagnetic or ferromagnetic interfacial coupling.

  3. Thermodynamic properties of Kagome antiferromagnets with different perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Rajiv R P [University of California, Davis, CA 95616 (United States); Rigol, Marcos, E-mail: singh@physics.ucdavis.ed [Georgetown University, 37th and O St NW, Washington, DC 20057 (United States)

    2009-01-01

    We discuss the results of several small perturbations to the thermodynamic properties of Kagome Lattice Heisenberg Model (KLHM) at high and intermediate temperatures, including Curie impurities, dilution, in-plane and out of plane Dzyaloshinski-Moria (DM) anisotropies and exchange anisotropy. We examine the combined role of Curie impurities and dilution in the behavior of uniform susceptibility. We also study the changes in specific heat and entropy with various anisotropies. Their relevance to newly discovered materials ZnCu{sub 3}(OH){sub 6}Cl{sub 2} is explored. We find that the magnetic susceptibility is well described by about 6 percent impurity and dilution. We also find that the entropy difference between the material and KLHM is well described by the DM parameter D{sub z}/J{approx}0:1.

  4. Canted antiferromagnetic ground state in Sr{sub 3}Ir{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Nagai, I [Japan Society for the Promotion of Science, Chiyoda, Tokyo 102-8471 (Japan); Yoshida, Y [Japan Society for the Promotion of Science, Chiyoda, Tokyo 102-8471 (Japan); Ikeda, S I [Nanoelectronics Research Institute AIST, Tsukuba, Ibaraki 305-8568 (Japan); Matsuhata, H [Nanoelectronics Research Institute AIST, Tsukuba, Ibaraki 305-8568 (Japan); Kito, H [Nanoelectronics Research Institute AIST, Tsukuba, Ibaraki 305-8568 (Japan); Kosaka, M [Faculty of Science, Saitama University, Saitama 305-8568 (Japan)

    2007-04-04

    We have characterized the ground state of Sr{sub 3}Ir{sub 2}O{sub 7} by performing measurements of electrical resistivity, magnetic susceptibility, magnetization, specific heat and electron diffraction (ED). Polycrystalline samples of Sr{sub 3}Ir{sub 2}O{sub 7} have been synthesized by using a high-pressure technique. Sr{sub 3}Ir{sub 2}O{sub 7} exhibits weak ferromagnetism with a small ferromagnetic component (2 x 10{sup -3} {mu}{sub B}/Ir) below T{sub C}{approx}280 K. The temperature dependence of the electrical resistivity {rho} shows semiconducting-like behaviour; d{rho}/dT<0 with an anomaly near T{sub C}. From the result for specific heat, a {lambda}-type anomaly appears at T{sub C}, indicating a second-order phase transition. The ED patterns below and above T{sub C} imply that there is no evidence of structural phase transition at T{sub C} with substantial symmetry change. These experimental results exclude the possibility of ferromagnetic ordering with extremely small magnetic moments below T{sub C}. Taking into account that certain pairs of Ir{sup 4+} ions lose the centre of inversion, this leads to the conclusion that the weak ferromagnetism is derived from canted antiferromagnetism.

  5. Doping of Ga in antiferromagnetic semiconductor α-Cr2O3 and its effects on magnetic and electronic properties

    Science.gov (United States)

    Bhowmik, R. N.; Venkata Siva, K.; Ranganathan, R.; Mazumdar, Chandan

    2017-06-01

    The samples of Ga-doped Cr2O3 have been prepared using chemical co-precipitation route. X-ray diffraction pattern and Raman spectra have indicated rhombohedral crystal structure with space group R 3 bar C. Magnetic measurements indicated diluted antiferromagnetic (AFM) spin order in Ga-doped α-Cr2O3 and ferrimagnetic ordering of spins at about 50-60 K is confirmed from the analysis of the temperature dependence of dc magnetization and ac susceptibility data. Apart from magnetic dilution effect, the samples have shown superparamagnetic behavior below 50 K due to frustrated surface spins of the nano-sized grains. The samples have shown non-linear electronic properties. The current-voltage (I-V) characteristics of the Ga-doped α-Cr2O3 samples are remarkably different from α-Cr2O3 sample. The bi-stable electronic states and negative differential resistance are some of the unique non-linear electronic properties that the I-V curves of Ga-doped samples have exhibited. Optical study revealed three electronic transitions in the samples associated with band gap energy at about 2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively. The results indicated multi-level electronic structure in Ga-doped α-Cr2O3 system.

  6. Effects of oxygen nonstoichiometry on the stability of antiferromagnetic phases of CuFeO2+δ single crystals

    Science.gov (United States)

    Hasegawa, M.; Batrashevich, M. I.; Zhao, T. R.; Takei, H.; Goto, T.

    2001-05-01

    Effects of oxygen nonstoichiometry on stabilities of the antiferromagnetic (AF) phases of CuFeO2 with a delafossite-type structure have been investigated. Temperature dependence of the magnetic susceptibility between 5 and 300 K in 0.1 T parallel to the c axis, and magnetic-field dependence of the magnetization below 40 T parallel to the c axis at 4.2 K are clarified using CuFeO2+δ single crystals with stoichiometry varying from oxygen deficiency (δ=-0.026, -0.061) to oxygen excess (δ=0.14, 0.085). It is found that the stabilities are strongly affected by the oxygen defects, depending on their type, i.e., oxygen deficiency or oxygen excess. The transition temperature between the four-sublattice AF phase (low-temperature AF phase) and the partially disordered phase (high-temperature AF phase) is increased by the oxygen deficiency, whereas it is decreased by the excess oxygen. It should be noted that both types of oxygen defects bring another metamagnetic transition around 23 T. Besides, all metamagnetic transition fields are increased by the oxygen defects. These effects are discussed from the viewpoints of crystal chemistry.

  7. The origin of the antiferromagnetic behaviour of the charge-transfer compound (HMTTF)[Ni(mnt)2].

    Science.gov (United States)

    Vela, Sergi; Fumanal, Maria; Deumal, Mercè

    2015-01-14

    The charge-transfer (HMTTF)[Ni(mnt)2] material (1) was the first mixed-stack compound reported to present ferromagnetic (FM) interactions between the donor (D) and acceptor (A) units within each mixed-stack. Despite the presence of a dominant FM interaction, its magnetic susceptibility curve, χ(T), corresponded to that of an antiferromagnetic (AFM) compound at low temperatures, a fact that was tentatively explained in terms of a FM-to-AFM magnetic transition. In this work, the First-Principles Bottom-Up procedure has been applied to rationalize the magnetic properties of 1. The results presented herein indicate the presence of up to five sizeable JAB magnetic exchange interactions (26.0, -1.7, 1.9, 0.1, and -99.3 cm(-1)) that create a complex 2D magnetic network. This magnetic topology not only produces a calculated χ(T) curve that is in excellent agreement with the experimental measurements, but also allows us to understand the magnetic behaviour of 1, in the full range of temperatures, solely in terms of the different Boltzmann population of diamagnetic and paramagnetic spin states as the temperature changes. Our data thus provide a plausible explanation for the AFM behaviour of 1 at low temperatures that does not involve a phase transition.

  8. Edge state magnetism in zigzag-interfaced graphene via spin susceptibility measurements.

    Science.gov (United States)

    Makarova, T L; Shelankov, A L; Zyrianova, A A; Veinger, A I; Tisnek, T V; Lähderanta, E; Shames, A I; Okotrub, A V; Bulusheva, L G; Chekhova, G N; Pinakov, D V; Asanov, I P; Šljivančanin, Ž

    2015-08-26

    Development of graphene spintronic devices relies on transforming it into a material with a spin order. Attempts to make graphene magnetic by introducing zigzag edge states have failed due to energetically unstable structure of torn zigzag edges. Here, we report on the formation of nanoridges, i.e., stable crystallographically oriented fluorine monoatomic chains, and provide experimental evidence for strongly coupled magnetic states at the graphene-fluorographene interfaces. From the first principle calculations, the spins at the localized edge states are ferromagnetically ordered within each of the zigzag interface whereas the spin interaction across a nanoridge is antiferromagnetic. Magnetic susceptibility data agree with this physical picture and exhibit behaviour typical of quantum spin-ladder system with ferromagnetic legs and antiferromagnetic rungs. The exchange coupling constant along the rungs is measured to be 450 K. The coupling is strong enough to consider graphene with fluorine nanoridges as a candidate for a room temperature spintronics material.

  9. Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3

    Science.gov (United States)

    Guo, Feng; Zhang, Na; Jin, Wei; Chang, Jun

    2017-06-01

    We theoretically study the dynamic time evolution following laser pulse pumping in an antiferromagnetic insulator Cr2O3. From the photoexcited high-spin quartet states to the long-lived low-spin doublet states, the ultrafast demagnetization processes are investigated by solving the dissipative Schrödinger equation. We find that the demagnetization times are of the order of hundreds of femtoseconds, in good agreement with recent experiments. The switching times could be strongly reduced by properly tuning the energy gaps between the multiplet energy levels of Cr3+. Furthermore, the relaxation times also depend on the hybridization of atomic orbitals in the first photoexcited state. Our results suggest that the selective manipulation of the electronic structure by engineering stress-strain or chemical substitution allows effective control of the magnetic state switching in photoexcited insulating transition-metal oxides.

  10. Weakening of antiferromagnetism due to frustration on inhomogeneous 2D lattices

    Energy Technology Data Exchange (ETDEWEB)

    Jagannathan, Anuradha, E-mail: jagannathan@lps.u-psud.f [Laboratoire de Physique des Solides, Universite Paris-Sud, 91405 Orsay (France)

    2009-01-01

    I consider the ground state of quantum spins interacting via Heisenberg antiferromagnetic exchange, in lattices having several types of local environment. In unfrustrated cases, when a Neel type order exists, it is known that quantum fluctuations are site-dependent, and lead to an inhomogeneous local staggered order parameter. This paper discusses some effects of adding frustration to such a system, by including next nearest neighbor antiferromagnetic interactions. Within linear spinwave theory, it is found that as the frustration parameter increases, the local order parameters decrease at a rate that depends on the type of sites involved in the frustrated loops. The cases of a decorated square lattice system, and of a quasiperiodic tiling are considered to study different ways in which antiferromagnetism is suppressed in these inhomogeneous systems.

  11. Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets

    KAUST Repository

    Železný, J.

    2014-10-06

    We predict that a lateral electrical current in antiferromagnets can induce nonequilibrium Néel-order fields, i.e., fields whose sign alternates between the spin sublattices, which can trigger ultrafast spin-axis reorientation. Based on microscopic transport theory calculations we identify staggered current-induced fields analogous to the intraband and to the intrinsic interband spin-orbit fields previously reported in ferromagnets with a broken inversion-symmetry crystal. To illustrate their rich physics and utility, we consider bulk Mn2Au with the two spin sublattices forming inversion partners, and a 2D square-lattice antiferromagnet with broken structural inversion symmetry modeled by a Rashba spin-orbit coupling. We propose an antiferromagnetic memory device with electrical writing and reading.

  12. Antiferromagnetic skyrmion crystals: Generation, topological Hall, and topological spin Hall effect

    Science.gov (United States)

    Göbel, Börge; Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2017-08-01

    Skyrmions are topologically nontrivial, magnetic quasiparticles that are characterized by a topological charge. A regular array of skyrmions, a skyrmion crystal (SkX), features the topological Hall effect (THE) of electrons, which, in turn, gives rise to the Hall effect of the skyrmions themselves. It is commonly believed that antiferromagnetic skyrmion crystals (AFM-SkXs) lack both effects. In this Rapid Communication, we present a generally applicable method to create stable AFM-SkXs by growing a two-sublattice SkX onto a collinear antiferromagnet. As an example we show that both types of skyrmion crystals, conventional and antiferromagnetic, exist in honeycomb lattices. While AFM-SkXs with equivalent lattice sites do not show a THE, they exhibit a topological spin Hall effect. On top of this, AFM-SkXs on inequivalent sublattices exhibit a nonzero THE, which may be utilized in spintronics devices. Our theoretical findings call for experimental realization.

  13. Entropy of diluted antiferromagnetic Ising models on frustrated lattices using the Wang-Landau method.

    Science.gov (United States)

    Shevchenko, Yuriy; Nefedev, Konstantin; Okabe, Yutaka

    2017-05-01

    We use a Monte Carlo simulation to study the diluted antiferromagnetic Ising model on frustrated lattices including the pyrochlore lattice to show the dilution effects. Using the Wang-Landau algorithm, which directly calculates the energy density of states, we accurately calculate the entropy of the system. We discuss the nonmonotonic dilution concentration dependence of residual entropy for the antiferromagnetic Ising model on the pyrochlore lattice, and compare it to the generalized Pauling approximation proposed by Ke et al. [Phys. Rev. Lett. 99, 137203 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.137203]. We also investigate other frustrated systems, the antiferromagnetic Ising model on the triangular lattice and the kagome lattice, demonstrating the difference in the dilution effects between the system on the pyrochlore lattice and that on other frustrated lattices.

  14. Exposure of the hidden anti-ferromagnetism in paramagnetic CdSe:Mn nanocrystals.

    Science.gov (United States)

    Zou, Shou-Jyun; Wang, Sheng-Tsung; Wu, Ming-Fan; Jian, Wen-Bin; Cheng, Shun-Jen

    2015-01-27

    We present theoretical and experimental investigations of the magnetism of paramagnetic semiconductor CdSe:Mn nanocrystals and propose an efficient approach to the exposure and analysis of the underlying anti-ferromagnetic interactions between magnetic ions therein. A key advance made here is the development of an analysis method with the exploitation of group theory technique that allows us to distinguish the anti-ferromagnetic interactions between aggregative Mn(2+) ions from the overall pronounced paramagnetism of magnetic-ion-doped semiconductor nanocrystals. By using the method, we clearly reveal and identify the signatures of anti-ferromagnetism from the measured temperature-dependent magnetisms and furthermore determine the average number of Mn(2+) ions and the fraction of aggregative ones in the measured CdSe:Mn nanocrystals.

  15. Inherited susceptibility and radiation exposure

    Energy Technology Data Exchange (ETDEWEB)

    Little, J.B. [Harvard School of Public Health, Boston, MA (United States)

    1997-03-01

    There is continuing concern that some people in the general population may have genetic makeups that place them at particularly high risk for radiation-induced cancer. The existence of such a susceptible subpopulation would have obvious implications for the estimation of risks of radiation exposure. Although it has been long known that familial aggregations of cancer do sometimes occur, recent evidence suggests that a general genetic predisposition to cancer does not exist; most cancers occur sporadically. On the other hand, nearly 10% of the known Mendelian genetic disorders are associated with cancer. A number of these involve a familial predisposition to cancer, and some are characterized by an enhanced susceptibility to the induction of cancer by various physical and chemical carcinogens, including ionizing radiation. Such increased susceptibility will depend on several factors including the frequency of the susceptibility gene in the population and its penetrance, the strength of the predisposition, and the degree to which the cancer incidence in susceptible individuals may be increased by the carcinogen. It is now known that these cancer-predisposing genes may be responsible not only for rare familial cancer syndromes, but also for a proportion of the common cancers. Although the currently known disorders can account for only a small fraction of all cancers, they serve as models for genetic predisposition to carcinogen-induced cancer in the general population. In the present report, the author describes current knowledge of those specific disorders that are associated with an enhanced predisposition to radiation-induced cancer, and discusses how this knowledge may bear on the susceptibility to radiation-induced cancer in the general population and estimates of the risk of radiation exposure.

  16. Critical Behaviour of Pure and Site-Random Two Dimensional Antiferromagnets

    DEFF Research Database (Denmark)

    Birgenau, R. J.; Als-Nielsen, Jens Aage; Shirane, G.

    1977-01-01

    Quasielastic neutron scattering studies of the static critical behavior in the two-dimensional antiferromagnets K2NiF4, K2MnF4, and Rb2Mn0.5Ni0.5F4 are reported. For T......Quasielastic neutron scattering studies of the static critical behavior in the two-dimensional antiferromagnets K2NiF4, K2MnF4, and Rb2Mn0.5Ni0.5F4 are reported. For T...

  17. Gyroscopic dynamics of antiferromagnetic vortices on domain boundaries of yttrium orthoferrite

    CERN Document Server

    Chetkin, M V; Shapaeva, T B

    2001-01-01

    It is experimentally established that the magnetic field along the b-axis weakly effects the velocity of the antiferromagnetic vortices on the domain boundary of the yttrium orthoferrite and doesn't explain the existence of the essential gyroscopic force, effecting these vortices. The existence of such a force is caused by the dynamic slope of the magnetic sublattices, proportional to the domain boundary velocity. The dynamics of the antiferromagnetic vortices in the yttrium orthoferrite domain boundaries is gyroscopic and quasirelativistic one with the threshold velocity of 20 km/s, equal to the spin waves velocity on the linear section of their dispersion law

  18. Spin-orbit torque in two-dimensional antiferromagnetic topological insulators

    Science.gov (United States)

    Ghosh, S.; Manchon, A.

    2017-01-01

    We investigate spin transport in two-dimensional ferromagnetic (FTI) and antiferromagnetic (AFTI) topological insulators. In the presence of an in-plane magnetization AFTI supports zero energy modes, which enables topologically protected edge conduction at low energy. We address the nature of current-driven spin torque in these structures and study the impact of spin-independent disorder. Interestingly, upon strong disorder the spin torque develops an antidamping component (i.e., even upon magnetization reversal) along the edges, which could enable current-driven manipulation of the antiferromagnetic order parameter. This antidamping torque decreases when increasing the system size and when the system enters the trivial insulator regime.

  19. Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers.

    Science.gov (United States)

    Wang, K; Sanderink, J G M; Bolhuis, T; van der Wiel, W G; de Jong, M P

    2015-10-21

    A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the rotation of antiferromagnetic moments of an insulating CoO layer, incorporated into a tunnel junction consisting of sapphire(substrate)/fcc-Co/CoO/AlOx/Al. The ferromagnetic Co layer is exchange coupled to the AFM CoO layer and drives rotation of the AFM moments in an external magnetic field. The results may help pave the way towards the development of spintronic devices based on AFM insulators.

  20. Magnetic Properties of Antiferromagnetic Oxide Materials Surfaces, Interfaces, and Thin Films

    CERN Document Server

    Duò, Lamberto; Ciccacci, Franco

    2010-01-01

    This first focused treatment on a hot topic highlights fundamental aspects as well as technological applications arising from a fascinating area of condensed matter physics. The editors have excellent track records and, in light of the broadness of the topic, retain the focus on antiferromagnetic oxides. They thus cover such topics as dichroism in x-ray absorption, non-magnetic substrates, exchange bias, ferromagnetic-antiferromagnetic interface coupling and oxide multilayers, as well as imaging using soft x-ray microscopy. The result is a very timely monograph for solid state physicists and c

  1. Spin-orbit torque in two-dimensional antiferromagnetic topological insulators

    KAUST Repository

    Ghosh, Sumit

    2017-01-24

    We investigate spin transport in two-dimensional ferromagnetic (FTI) and antiferromagnetic (AFTI) topological insulators. In the presence of an in-plane magnetization AFTI supports zero energy modes, which enables topologically protected edge conduction at low energy. We address the nature of current-driven spin torque in these structures and study the impact of spin-independent disorder. Interestingly, upon strong disorder the spin torque develops an antidamping component (i.e., even upon magnetization reversal) along the edges, which could enable current-driven manipulation of the antiferromagnetic order parameter. This antidamping torque decreases when increasing the system size and when the system enters the trivial insulator regime.

  2. Quantum critical point in the Sc-doped itinerant antiferromagnet TiAu

    Science.gov (United States)

    Svanidze, E.; Besara, T.; Wang, J. K.; Geiger, D.; Prochaska, L.; Santiago, J. M.; Lynn, J. W.; Paschen, S.; Siegrist, T.; Morosan, E.

    2017-06-01

    We present an experimental realization of a quantum critical point in an itinerant antiferromagnet composed of nonmagnetic constituents, TiAu. By partially substituting Ti with Sc in Ti1 -xScxAu , a doping amount of xc=0.13 ±0.01 induces a quantum critical point with minimal disorder effects. The accompanying non-Fermi liquid behavior is observed in both the resistivity ρ ∝T and specific heat Cp/T ∝-ln T , characteristic of a two-dimensional antiferromagnet. The quantum critical point is accompanied by an enhancement of the spin fluctuations, as indicated by the diverging Sommerfeld coefficient γ at x =xc .

  3. Three-state anti-ferromagnetic Potts model in three dimensions universality and critical amplitudes

    CERN Document Server

    Gottlob, A P

    1994-01-01

    We present the results of a Monte Carlo study of the three-dimensional anti-ferromagnetic 3-state Potts model. We compute various cumulants in the neighbourhood of the critical coupling. The comparison of the results with a recent high statistics study of the 3D XY model strongly supports the hypothesis that both models belong to the same universality class. From our numerical data for the anti-ferromagnetic 3-state Potts model we obtain for the critical coupling \\coup_c=0.81563(3), and for the static critical exponents .gamma. /.nu. = 1.973(9) and .nu. = 0.664(4).

  4. Susceptibility to malignant hyperthermia

    NARCIS (Netherlands)

    Snoeck, Marcus Matheus Johannes

    2004-01-01

    In this thesis the author studied the diagnostic procedures for susceptibility to malignant hyperthermia (MH), with special emphasis upon refining the biological diagnostic test and improving protocols and guidelines for investigation of MH susceptibility. MH is a pharmacogenetic disease of skeletal

  5. Antiferromagnetic structure and electronic properties of BaCr2As2 and BaCrFeAs2

    Science.gov (United States)

    Filsinger, Kai A.; Schnelle, Walter; Adler, Peter; Fecher, Gerhard H.; Reehuis, Manfred; Hoser, Andreas; Hoffmann, Jens-Uwe; Werner, Peter; Greenblatt, Martha; Felser, Claudia

    2017-05-01

    Recent theoretical studies suggest that superconductivity may be found in doped chromium pnictides with crystal structures similar to their iron counterparts. Here, we report a comprehensive study on the magnetic arsenides BaCr2As2 and BaCrFeAs2 (space group I 4 /m m m ), which are possible mother compounds with d4 and d5 electron configurations, respectively. DFT-based calculations of the electronic structure evidence metallic antiferromagnetic ground states for both compounds. By powder neutron diffraction, we confirm for BaCr2As2 a robust ordering in the antiferromagnetic G -type structure at TN=580 K with μCr=1.9 μB . Anomalies in the lattice parameters point to magnetostructural coupling effects. In BaCrFeAs2, the Cr and Fe atoms randomly occupy the transition-metal site and G -type order is found below 265 K with μCr /Fe=1.1 μB . 57Fe Mössbauer spectroscopy demonstrates that only a small ordered moment is associated with the Fe atoms, in agreement with electronic structure calculations leading to μFe˜0 . The temperature dependence of the hyperfine field does not follow that of the total moments. Both compounds are metallic but show large enhancements of the linear specific heat. Electrical transport in BaCrFeAs2 is dominated by the atomic disorder and the partial magnetic disorder of Fe. Our results indicate that Néel-type order is unfavorable for Fe moments and thus it is destabilized with increasing Fe content.

  6. Multiple charge density wave transitions in the antiferromagnets R NiC2 (R =Gd ,Tb)

    Science.gov (United States)

    Shimomura, S.; Hayashi, C.; Hanasaki, N.; Ohnuma, K.; Kobayashi, Y.; Nakao, H.; Mizumaki, M.; Onodera, H.

    2016-04-01

    X-ray scattering and electrical resistivity measurements were performed on GdNiC2 and TbNiC2. We found a set of satellite peaks characterized by q1=(0.5 ,η ,0 ) below T1, at which the resistivity shows a sharp inflection, suggesting the charge density wave (CDW) formation. The value of η decreases with decreasing temperature below T1, and then a transition to a commensurate phase with q1 C=(0.5 ,0.5 ,0 ) takes place. The diffuse scattering observed above T1 indicates the presence of soft phonon modes associated with CDW instabilities at q1 and q2=(0.5 ,0.5 ,0.5 ) . The long-range order given by q2 is developed in addition to that given by q1 C in TbNiC2, while the short-range correlation with q2 persists even at 6 K in GdNiC2. The amplitude of the q1 C lattice modulation is anomalously reduced below an antiferromagnetic transition temperature TN in GdNiC2. In contrast, the q2 order vanishes below TN in TbNiC2. We demonstrate that R NiC2 (R = rare earth) compounds exhibit similarities with respect to their CDW phenomena, and discuss the effects of magnetic transitions on CDWs. We offer a possible displacement pattern of the modulated structure characterized by q1 C and q2 in terms of frustration.

  7. GPU-Accelerated Population Annealing Algorithm: Frustrated Ising Antiferromagnet on the Stacked Triangular Lattice

    Directory of Open Access Journals (Sweden)

    Borovský Michal

    2016-01-01

    Full Text Available The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = −1. The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.

  8. Singlet Ground State Magnetism: III Magnetic Excitons in Antiferromagnetic TbP

    DEFF Research Database (Denmark)

    Knorr, K.; Loidl, A.; Kjems, Jørgen

    1981-01-01

    The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined....

  9. 't Hooft-Polyakov monopoles in an antiferromagnetic Bose-Einstein condensate

    NARCIS (Netherlands)

    Stoof, H.T.C.; Vliegen, E.; Al Khawaja, U.

    2001-01-01

    We show that an antiferromagnetic spin-1 Bose-Einstein condensate, which can for instance be created with 23-Na atoms in an optical trap, has not only singular line-like vortex excitations, but also allows for singular point-like topological excitations, i.e., 't Hooft-Polyakov monopoles. We discuss

  10. The dynamical frustration of interlayer excitons delocalizing in bilayer quantum antiferromagnets

    NARCIS (Netherlands)

    Rademaker, L.; Wu, K.; Hilgenkamp, H.; Zaanen, J.

    2012-01-01

    Using the self-consistent Born approximation we study the delocalization of interlayer excitons in the bilayer Heisenberg quantum antiferromagnet. Under realistic conditions we find that the coupling between the exciton motion and the spin system is strongly enhanced as compared to the case of a

  11. Influence of atomic ordering on the Fe{sub 2}Nb antiferromagnetic alloy

    Energy Technology Data Exchange (ETDEWEB)

    Vélez, G.Y., E-mail: g.y.velezcastillo@gmail.com; Alcázar, G.A. Pérez; Zamora, Ligia E.

    2014-03-15

    Fe{sub 2}Nb samples were obtained by arc melting, ordered by heat treatment, and finally disordered by means of mechanical alloying with milling times of 0.5, 1, 2 and 4 h. The ordered alloy shows only the hcp-Fe{sub 2}Nb structure which is paramagnetic at room temperature, and at low temperatures exhibits spin glass and antiferromagnetic behaviours. Mechanical alloying destroys the ordered structure and permits the formation of bcc iron-rich grains. Atomic disorder maintains the antiferromagnetic behaviour of the alloy, but increases its freezing temperature. The Néel temperature of the hcp grains is increased by the apparition of bcc grains. - Highlights: • By means of arc-melting the ordered Fe{sub 2}Nb alloy was obtained. • The ordered Fe{sub 2}Nb alloy exhibits antiferromagnetic behaviour. • Atomic disorder does not affect the antiferromagnetic phase of the alloy. • Néel temperature increases only due to the formation of the bcc Fe–Nb grains that appear during mechanical alloying.

  12. High-frequency effects in antiferromagnetic Sr3Ir2O7

    Science.gov (United States)

    Williamson, Morgan; Seinige, Heidi; Shen, Shida; Wang, Cheng; Cao, Gang; Zhou, Jianshi; Goodenough, John; Tsoi, Maxim

    Antiferromagnetic (AFM) spintronics is one of many promising routes for `beyond the CMOS' technologies where unique properties of AFM materials are exploited to achieve new and improved functionalities. AFMs are especially interesting for high-speed memory applications thanks to their high natural frequencies. Here we report the effects of high-frequency (microwave) currents on transport properties of antiferromagnetic Mott insulator Sr3Ir2O7. The microwaves at 3-7 GHz were found to affect the material's current-voltage characteristic and produce resonance-like features that we tentatively associate with the dissipationless magnonics recently predicted to occur in antiferromagnetic insulators subject to ac electric fields. Our observations support the potential of antiferromagnetic materials for high-speed/high-frequency spintronic applications. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, by NSF Grants DMR-1207577, DMR-1265162, DMR-1600057, and DMR-1122603, and by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2015-CRG4-2626.

  13. The magnetic properties of antiferromagnetic nanoparticles: NiO and -Fe2O3

    DEFF Research Database (Denmark)

    Bahl, Christian Robert Haffenden

    2006-01-01

    Nikkel oxid (NiO) og hematit -Fe2O3) er begge antiferromagneter med magnetiske egenskaber på nanoskala, som er forskellige fra dem i større krystaller. Med hovedvægt på nanopartikler af NiO og sammenligninger med nanopartikler af hematit studeres disse magnetiske egenskaber med en række...

  14. Antiferromagnetic transition in Ru2CrSi in magnetic fields

    Science.gov (United States)

    Hiroi, Masahiko; Uchida, Kaori; Shigeta, Iduru; Ito, Masakazu; Koyama, Keiichi; Kimura, Shojiro; Watanabe, Kazuo

    2013-06-01

    In the Heusler compound Ru2CrSi, an antiferromagnetic transition at T N =14 K was revealed by specific heat and magnetization measurements. In this study the electrical resistivity is measured in magnetic fields up to 14.5 T, and the antiferromagnetic transition in magnetic fields is investigated. In the temperature dependence of the resistivity at zero field, a clear dip at ˜15 K and a hump with a maximum at ˜ 9 K are observed. This dip is considered to be due to the antiferromagnetic transition. With increasing magnetic field, the magnitude of the resistivity slightly increases around T N ; i.e., a positive magnetoresistance is observed. The temperature dependence of the resistivity is hardly affected by increasing the magnetic field. The transition temperature decreases only by ˜ 0.3 K even with applying 14.5 T. These results demonstrate that the antiferromagnetic state in Ru2CrSi is unusually unaffected by a strong magnetic field.

  15. Influence of a transport current on a domain wall in an antiferromagnetic metal

    NARCIS (Netherlands)

    Swaving, A.C.; Duine, R.A.

    2011-01-01

    Part of Special issue on domain wall dynamics in nanostructures We consider the influence of an electric current on the position of a domain wall in an antiferromagnetic metal. We first microscopically derive an equation of motion for the Néel vector in the presence of current by performing, in the

  16. Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer

    Science.gov (United States)

    Gross, I.; Akhtar, W.; Garcia, V.; Martínez, L. J.; Chouaieb, S.; Garcia, K.; Carrétéro, C.; Barthélémy, A.; Appel, P.; Maletinsky, P.; Kim, J.-V.; Chauleau, J. Y.; Jaouen, N.; Viret, M.; Bibes, M.; Fusil, S.; Jacques, V.

    2017-09-01

    Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

  17. Spin freezing in the geometrically frustrated pyrochlore antiferromagnet Tb2Mo2O7

    DEFF Research Database (Denmark)

    Gaulin, B.D.; Reimers, J.N.; Mason, T.E.

    1992-01-01

    The magnetic metal ions in the cubic pyrochlore Tb2Mo2O7 form an infinite three-dimensional network of corner-sharing tetrahedra with a very high potential for frustration in the presence of antiferromagnetism. We have performed neutron scattering measurements which show short-range spatial corre...

  18. Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers

    NARCIS (Netherlands)

    Wang, Kai; Sanderink, Johannes G.M.; Bolhuis, Thijs; van der Wiel, Wilfred Gerard; de Jong, Machiel Pieter

    2015-01-01

    A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the

  19. Half-magnetization plateau in a Heisenberg antiferromagnet on a triangular lattice

    Science.gov (United States)

    Ye, Mengxing; Chubukov, Andrey V.

    2017-10-01

    We present the phase diagram of a 2D isotropic triangular Heisenberg antiferromagnet in a magnetic field. We consider spin-S model with nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions. We focus on the range of 1 /8 border the "three up, one down" state and discuss the transitions between these states and the canted stripe state.

  20. Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain

    DEFF Research Database (Denmark)

    Stone, M.B.; Reich, D.H.; Broholm, C.

    2003-01-01

    Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...

  1. Domain Wall Magnetoresistance and Complex Magnetic Response in Antiferromagnetically Coupled Fe/Cr Multilayers

    Science.gov (United States)

    2003-01-01

    Antiferromagnetically Coupled Fe/Cr Multilayers F.G.Aliev1, R.Villar1, R.Schad2 and J.L.Martinez 3 (1) Dpto. de Fisica de la Materia Condensada, C-Ill...Universidad Aut6noma de Madrid, 28049, Madrid, Spain (2) CMIT, University of Alabama, Tuscaloosa, USA (3) Instituto de Ciencia de Materiales Madrid

  2. Antiferromagnetic order in superconducting UPt[sub 3]: An x-ray magnetic scattering study (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Isaacs, E.D. (AT T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (United States)); Zschack, P. (Oak Ridge Institute for Science and Education, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Ramirez, A.P.; Oglesby, C.S.; Bucher, E. (AT T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (United States))

    1994-11-15

    The temperature dependence of the antiferromagnetic order in superconducting UPt[sub 3] has been measured using x-ray resonance magnetic scattering. The magnetic Bragg intensity at [ital Q]=(1/2,0,2) grows linearly from [ital T][sub [ital N

  3. Spin-orbit torques in locally and globally noncentrosymmetric crystals: Antiferromagnets and ferromagnets

    KAUST Repository

    Železný, J.

    2017-01-10

    One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný, Phys. Rev. Lett. 113, 157201 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley, Science 351, 587 (2016)]SCIEAS0036-807510.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.

  4. Quantum Spin Liquid in the Kagome-Lattice Antiferromagnet and Related Systems

    Science.gov (United States)

    Nakano, Hiroki; Sakai, Tôru

    2017-06-01

    The S=1/2 kagome-lattice antiferromagnet is investigated using the numerical diagonalization up to the 42-spin cluster. The analysis of the field derivative of the magnetization at the zero magnetization indicates that the magnetic excitation ot the system is gapless. It is consistent with our previous finite-scaling analysis of the spin gap.

  5. Griffiths singularities in the random quantum Ising antiferromagnet: A tree tensor network renormalization group study

    Science.gov (United States)

    Lin, Yu-Ping; Kao, Ying-Jer; Chen, Pochung; Lin, Yu-Cheng

    2017-08-01

    The antiferromagnetic Ising chain in both transverse and longitudinal magnetic fields is one of the paradigmatic models of a quantum phase transition. The antiferromagnetic system exhibits a zero-temperature critical line separating an antiferromagnetic phase and a paramagnetic phase; the critical line connects an integrable quantum critical point at zero longitudinal field and a classical first-order transition point at zero transverse field. Using a strong-disorder renormalization group method formulated as a tree tensor network, we study the zero-temperature phase of the quantum Ising chain with bond randomness. We introduce a new matrix product operator representation of high-order moments, which provides an efficient and accurate tool for determining quantum phase transitions via the Binder cumulant of the order parameter. Our results demonstrate an infinite-randomness quantum critical point in zero longitudinal field accompanied by pronounced quantum Griffiths singularities, arising from rare ordered regions with anomalously slow fluctuations inside the paramagnetic phase. The strong Griffiths effects are signaled by a large dynamical exponent z >1 , which characterizes a power-law density of low-energy states of the localized rare regions and becomes infinite at the quantum critical point. Upon application of a longitudinal field, the quantum phase transition between the paramagnetic phase and the antiferromagnetic phase is completely destroyed. Furthermore, quantum Griffiths effects are suppressed, showing z <1 , when the dynamics of the rare regions is hampered by the longitudinal field.

  6. The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet

    CERN Document Server

    Cherepanov, V B; Podivilov, E V

    2001-01-01

    The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance

  7. Reducing Susceptibility to Courtesy Stigma.

    Science.gov (United States)

    Bachleda, Catherine L; El Menzhi, Leila

    2017-04-19

    In light of the chronic shortage of health professionals willing to care for HIV/AIDS patients, and rising epidemics in many Muslim countries, this qualitative study examined susceptibility and resistance to courtesy stigma as experienced by nurses, doctors, and social workers in Morocco. Forty-nine in-depth interviews provided rich insights into the process of courtesy stigma and how it is managed, within the context of interactions with Islam, interactions within the workplace (patients, other health professionals), and interactions outside the workplace (the general public, friends, and family). Theoretically, the findings extend understanding of courtesy stigma and the dirty work literature. The findings also offer practical suggestions for the development of culturally appropriate strategies to reduce susceptibility to courtesy stigmatization. This study represents the first to explore courtesy stigma as a process experienced by health professionals providing HIV/AIDS care in an Islamic country.

  8. Health service marketing: a suggested model.

    Science.gov (United States)

    Zaltman, G; Vertinsky, I

    1971-07-01

    Focus is on social marketing in a health context, and attention is directed to the development of a psychosocial model of health-related behavior with emphasis on developing countries. Each component of the model is identified and defined, with some of the interactions among its components noted. There are both advantages and limitations to using the model in a social marketing context. The model's primary contribution at this stage of its development is in structuring and organizing diverse sources of knowledge and data. New relationships are suggested which were not previously considered in the literature. The relationship between risk-taking and perceived susceptibility is 1 example. The model also provides a basis for simulating health processes, providing a testing ground for health policies before their actual implementation. The model's perspective is uniquely appropriate for the development of social marketing strategies, and it promises to encompass health market behavior in various cultural settings.

  9. Deepening sleep by hypnotic suggestion.

    Science.gov (United States)

    Cordi, Maren J; Schlarb, Angelika A; Rasch, Björn

    2014-06-01

    Slow wave sleep (SWS) plays a critical role in body restoration and promotes brain plasticity; however, it markedly declines across the lifespan. Despite its importance, effective tools to increase SWS are rare. Here we tested whether a hypnotic suggestion to "sleep deeper" extends the amount of SWS. Within-subject, placebo-controlled crossover design. Sleep laboratory at the University of Zurich, Switzerland. Seventy healthy females 23.27 ± 3.17 y. Participants listened to an auditory text with hypnotic suggestions or a control tape before napping for 90 min while high-density electroencephalography was recorded. After participants listened to the hypnotic suggestion to "sleep deeper" subsequent SWS was increased by 81% and time spent awake was reduced by 67% (with the amount of SWS or wake in the control condition set to 100%). Other sleep stages remained unaffected. Additionally, slow wave activity was significantly enhanced after hypnotic suggestions. During the hypnotic tape, parietal theta power increases predicted the hypnosis-induced extension of SWS. Additional experiments confirmed that the beneficial effect of hypnotic suggestions on SWS was specific to the hypnotic suggestion and did not occur in low suggestible participants. Our results demonstrate the effectiveness of hypnotic suggestions to specifically increase the amount and duration of slow wave sleep (SWS) in a midday nap using objective measures of sleep in young, healthy, suggestible females. Hypnotic suggestions might be a successful tool with a lower risk of adverse side effects than pharmacological treatments to extend SWS also in clinical and elderly populations.

  10. Wavevector-Dependent Susceptibility in Quasiperiodic Ising Models

    Science.gov (United States)

    Au-Yang, Helen; Jin, Bai-Qi; Perk, Jacques H. H.

    2001-02-01

    Using the various functional relations for correlation functions in planar Ising models, new results are obtained for the correlation functions and the q-dependent susceptibility for Ising models on a quadratic lattice with quasiperiodic coupling constants. The effects are clearest if the interactions are both attractive and repulsive according to a quasiperiodic pattern. In particular, an exact scaling limit result for the two-point correlation function of the Z-invariant inhomogeneous Ising model is presented and the q-dependent susceptibility is calculated for some cases where the coupling constants vary according to Fibonacci rules. It is found that the ferromagnetic case differs drastically from the case with both ferro- and antiferromagnetic bonds. In the mixed case, the peaks of the q-dependent susceptibility are everywhere dense for temperature T both above or below the critical temperature Tc, but due to overlap only a finite number of peaks is visible. This number of visible peaks decreases as T moves away from Tc. In the ferromagnetic case, there is typically only one single peak at q=0, in spite of the aperiodicity present in the lattice. These results provide evidence that in real systems, even if the atoms arrange themselves aperiodically, there will be no dramatic difference in the diffraction pattern, unless the pair correlation function has clear aperiodic oscillations. The number of oscillations per correlation length determines the number of visible peaks.

  11. Effects of magnetic interactions in antiferromagnetic ferrihydrite particles

    Energy Technology Data Exchange (ETDEWEB)

    Berquo, Thelma S; Banerjee, Subir K [Institute for Rock Magnetism, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Erbs, Jasmine J; Penn, R Lee [Department of Chemistry, University of Minnesota, Minneapolis, MN 55455 (United States); Lindquist, Anna [Department of Physics, Gustavus Adolphus College, Saint Peter, MN 56082 (United States)], E-mail: berqu013@umn.edu

    2009-04-29

    The effects of magnetic interactions in the magnetic properties of six-line ferrihydrite particles were investigated by studying the behavior of aggregated versus coated particles. Four different coating agents (sugar, alginate, lactate and ascorbate) were employed in order to obtain dispersed particles and prevent particle agglomeration; one sub-sample was allowed to dry with no coating agent. The five sets of ferrihydrite particles were from the same batch and the size was estimated as 3.6 {+-} 0.4 nm in length. Low temperature magnetization, ac susceptibility and Moessbauer spectroscopy data showed contrasting blocking temperatures for uncoated and coated samples with a decrease of T{sub P} from about 50 K to 12 K, respectively. The contributions from magnetic interactions were recognized in magnetic measurements and the effective anisotropy constant for non-interacting ferrihydrite was estimated as (100 {+-} 10) x 10{sup 3} J m{sup -3}. Overall, employing sugar and alginate as coating agents was more successful in preventing particle aggregation and magnetic interactions. In contrast, ascorbate and lactate were unsuitable due to the chemical reaction between the coating agent and ferrihydrite surface.

  12. Deepening Sleep by Hypnotic Suggestion

    Science.gov (United States)

    Cordi, Maren J.; Schlarb, Angelika A.; Rasch, Björn

    2014-01-01

    Study Objectives: Slow wave sleep (SWS) plays a critical role in body restoration and promotes brain plasticity; however, it markedly declines across the lifespan. Despite its importance, effective tools to increase SWS are rare. Here we tested whether a hypnotic suggestion to “sleep deeper” extends the amount of SWS. Design: Within-subject, placebo-controlled crossover design. Setting: Sleep laboratory at the University of Zurich, Switzerland. Participants: Seventy healthy females 23.27 ± 3.17 y. Intervention: Participants listened to an auditory text with hypnotic suggestions or a control tape before napping for 90 min while high-density electroencephalography was recorded. Measurements and Results: After participants listened to the hypnotic suggestion to “sleep deeper” subsequent SWS was increased by 81% and time spent awake was reduced by 67% (with the amount of SWS or wake in the control condition set to 100%). Other sleep stages remained unaffected. Additionally, slow wave activity was significantly enhanced after hypnotic suggestions. During the hypnotic tape, parietal theta power increases predicted the hypnosis-induced extension of SWS. Additional experiments confirmed that the beneficial effect of hypnotic suggestions on SWS was specific to the hypnotic suggestion and did not occur in low suggestible participants. Conclusions: Our results demonstrate the effectiveness of hypnotic suggestions to specifically increase the amount and duration of slow wave sleep (SWS) in a midday nap using objective measures of sleep in young, healthy, suggestible females. Hypnotic suggestions might be a successful tool with a lower risk of adverse side effects than pharmacological treatments to extend SWS also in clinical and elderly populations. Citation: Cordi MJ, Schlarb AA, Rasch B. Deepening sleep by hypnotic suggestion. SLEEP 2014;37(6):1143-1152. PMID:24882909

  13. Magnetic susceptibility of the rare earth element impurities in the IV-VI semiconductors and Curie-Weiss law

    Energy Technology Data Exchange (ETDEWEB)

    Zayachuk, D.M., E-mail: zayachuk@polynet.lviv.u [Lviv Polytechnic National University, 12 Bandera Street, 79013 Lviv (Ukraine)

    2010-01-15

    Peculiarities of applying the Curie-Weiss law to the analysis of the magnetic susceptibility of the impurities of the rare earth elements in the IV-VI crystals are examined. It is shown that the traditional approach to the determination of the paramagnetic Curie temperature of ferromagnets and antiferromagnets applied to the impurities of ferromagnetic and antiferromagnetic elements in the doped crystal may lead to fundamental mistakes. The results of this examination are used to analyze the high temperature magnetic susceptibility of Eu and Gd impurities in the PbTe doped crystals grown from the melt using the Bridgman method. It is established that the doping of PbTe with Eu leads to the formation of ferromagnetic inclusions and the same doping with Gd leads to the formation of antiferromagnetic inclusions in the crystal. It is shown that these inclusions are most likely the complexes based on the europium or gadolinium oxides EuO and Gd{sub 2}O{sub 3}, respectively.

  14. Orbitally induced hierarchy of exchange interactions in the zigzag antiferromagnetic state of honeycomb silver delafossite Ag3Co2SbO6.

    Science.gov (United States)

    Zvereva, E A; Stratan, M I; Ushakov, A V; Nalbandyan, V B; Shukaev, I L; Silhanek, A V; Abdel-Hafiez, M; Streltsov, S V; Vasiliev, A N

    2016-04-25

    We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN ∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin-flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co-Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co(2+) ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite.

  15. Antiferromagnetism in semiconducting SrMn2Sb2 and BaMn2Sb2 single crystals

    Science.gov (United States)

    Sangeetha, N. S.; Smetana, V.; Mudring, A.-V.; Johnston, D. C.

    2018-01-01

    Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ , heat capacity Cp, and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M (H ) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2 -type structure, whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2 -type structure. The ρ (T ) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2 . The χ (T ) and Cp(T ) data reveal antiferromagnetic (AFM) ordering at TN = 110 K for SrMn2Sb2 and 450 K for BaMn2Sb2 . The anisotropic χ (T ≤TN) data also show that the ordered moments in SrMn2Sb2 are aligned in the hexagonal a b plane, whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the tetragonal c axis. The a b -plane M (H ) data for SrMn2Sb2 exhibit a continuous metamagnetic transition at low fields 0 literature for Mn pnictides with the CaAl2Si2 and ThCr2Si2 crystal structures show that the TN values for the CaAl2Si2 -type compounds are much smaller than those for the ThCr2Si2 -type materials.

  16. Exact Critical Exponents for the Antiferromagnetic Quantum Critical Metal in Two Dimensions

    Science.gov (United States)

    Schlief, Andres; Lunts, Peter; Lee, Sung-Sik

    2017-04-01

    Unconventional metallic states which do not support well-defined single-particle excitations can arise near quantum phase transitions as strong quantum fluctuations of incipient order parameters prevent electrons from forming coherent quasiparticles. Although antiferromagnetic phase transitions occur commonly in correlated metals, understanding the nature of the strange metal realized at the critical point in layered systems has been hampered by a lack of reliable theoretical methods that take into account strong quantum fluctuations. We present a nonperturbative solution to the low-energy theory for the antiferromagnetic quantum critical metal in two spatial dimensions. Being a strongly coupled theory, it can still be solved reliably in the low-energy limit as quantum fluctuations are organized by a new control parameter that emerges dynamically. We predict the exact critical exponents that govern the universal scaling of physical observables at low temperatures.

  17. Direct evidence of imprinted vortex states in the antiferromagnet of exchange biased microdisks

    Science.gov (United States)

    Salazar-Alvarez, G.; Kavich, J. J.; Sort, J.; Mugarza, A.; Stepanow, S.; Potenza, A.; Marchetto, H.; Dhesi, S. S.; Baltz, V.; Dieny, B.; Weber, A.; Heyderman, L. J.; Nogués, J.; Gambardella, P.

    2009-07-01

    The magnetic domain structure of patterned antiferromagnetic/ferromagnetic Ir20Mn80/Ni80Fe20 bilayer microdisk arrays has been investigated using layer-specific polarized x-ray photoemission electron microscopy and magnetic circular dichroism. Magnetic imaging at the Fe and Mn L-edge resonances provided direct evidence of a vortex state imprinted into the antiferromagnet at the interface. The opposite magnetic contrast between the layers indicated a reversed chirality of the imprinted vortex state, and a quantitative analysis of the magnetic moment from the dichroism spectra showed that uncompensated Mn spins equivalent to about 60% of a monolayer of bulk Ir20Mn80 contributed to the imprinted information at the interface.

  18. Theoretical Analysis of Inertia-like Switching in Magnets: Applications to a Synthetic Antiferromagnet

    Directory of Open Access Journals (Sweden)

    Satadeep Bhattacharjee

    2012-03-01

    Full Text Available The magnetization dynamics of a synthetic antiferromagnet subjected to a short-magnetic-field pulse has been studied by using a combination of first principles calculations and atomistic spin-dynamics simulations. We observe switching phenomena on the time scale of tens of picoseconds, and inertia-like behavior in the magnetization dynamics. We explain the latter in terms of a dynamic redistribution of magnetic energy from the applied-field pulse to other possible energy terms, such as the exchange interaction and the magnetic anisotropy, without invoking concepts such as the inertia of an antiferromagnetic vector. We also demonstrate that such dynamics can also be observed in a ferromagnetic material where the incident-field pulse pumps energy to the magnetic anisotropy.

  19. Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films

    Science.gov (United States)

    Cossu, F.; Schwingenschlögl, U.; Colizzi, G.; Filippetti, A.; Fiorentini, Vincenzo

    2013-06-01

    Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.

  20. Mott Transition, Antiferromagnetism, and d-wave Superconductivity in Two-Dimensional Organic Conductors

    Science.gov (United States)

    Tremblay, A.-M. S.; Kyung, Bumsoo

    2007-03-01

    We study the Mott transition, antiferromagnetism and superconductivity in layered organic conductors using Cellular Dynamical Mean Field Theory for the frustrated Hubbard model. A d-wave superconducting phase appears between an antiferromagnetic insulator and a metal for t^'/t=0.3-0.7 , or between a nonmagnetic Mott insulator (spin liquid) and a metal for t^'/t>=0.8, in agreement with experiments on layered organic conductors including κ-(ET)2Cu2(CN)3. These phases are separated by a strong first order transition. The phase diagram gives much insight into the mechanism for d-wave superconductivity. Two predictions are made. B. Kyung and A.-M.S. Tremblay, Phys. Rev. Lett. 97, 046402 (2006)

  1. A continuous analysis for the antiferromagnetic Heisenberg model on the checkerboard lattice

    Science.gov (United States)

    Moura, A. R.; Pereira, A. R.

    2017-11-01

    In this paper we investigate the antiferromagnetic Heisenberg model on the checkerboard lattice by the O (3) Non-linear Sigma Model (NLSM). The checkerboard lattice is distinguished from the antiferromagnetic square lattice (with coupling constant J) by the presence of diagonal crossing (with coupling constant J‧) in half of the sites. This lattice model is the direct analogous of the three-dimensional pyrochlore lattice in a two-dimensional surface. Many effects of the three-dimensional model version, as the Quantum Order-by-Disorder, have been recently described also in the checkerboard lattice. Here we have developed the continuous version of the Heisenberg model on the checkerboard lattice and applied Renormalization Group together other techniques to analyze the both cases J J‧. We have therefore determined the effects of the crossing interaction J‧ on the phase transitions. In addition, skyrmion solutions and their possible influences on these transitions were also considered.

  2. Effective Hamiltonian and low-lying eigenenergy clustering patterns of four-sublattice antiferromagnets

    DEFF Research Database (Denmark)

    Zhang, N.G.; Henley, C.L.; Rischel, C.

    2002-01-01

    We study the low-lying eigenenergy clustering patterns of quantum antiferromagnets with p sublattices (in particular p = 4). We treat each sublattice as a large spin, and using second-order degenerate perturbation theory, we derive the effective (biquadratic) Hamiltonian coupling the p large spins....... In order to compare with exact diagonalizations, the Hamiltonian is explicitly written for a finite-size lattice, and it contains information on energies of excited states as well as the ground state. The result is applied to the face-centered-cubic Type-I antiferromagnet of spin 1/2, including second......-neighbor interactions. A 32-site system is exactly diagonalized, and the energy spectrum of the low-lying singlets follows the analytically predicted clustering pattern....

  3. Electronic and optical properties of antiferromagnetic iron doped NiO – A first principles study

    Directory of Open Access Journals (Sweden)

    John E. Petersen

    2017-05-01

    Full Text Available Antiferromagnetic NiO is a candidate for next generation high-speed and scaled RRAM devices. Here, electronic and optical properties of antiferromagnetic NiO: Fe 25% in the rock salt structure are studied and compared to intrinsic NiO. From density of states and complex dielectric function analysis, the first optical transition is found to be at lower frequency than intrinsic NiO due to an Fe impurity level being the valence band maximum. The resulting effects on refractive index, reflectivity, absorption, optical conductivity and loss function for Fe-doped NiO are compared to those of intrinsic NiO, and notable differences are analyzed. The electronic component of the static dielectric constant of NiO: Fe 25% is calculated to be about 2% less than that of intrinsic NiO.

  4. Magnetization process in the antiferromagnet URu sub 2 Si sub 2

    Energy Technology Data Exchange (ETDEWEB)

    Radwanski, R.J. (Van der Waals-Zeeman Lab., Univ. Amsterdam (Netherlands))

    1992-01-01

    The Crystalline-Electric-Field (CEF) based approach with a non-magnetic singlet vertical stroke-2> -vertical stroke+2>, resulting from higher-order CEF interactions, as the ground state for the {sup 3}H{sub 4} multiplet of the U{sup 4+} ion provides a very consistent explanation for many experimental features of URu{sub 2}Si{sub 2}. The magnetization process in URu{sub 2}Si{sub 2} is discussed in terms of the formation of the U{sup 4+}-ion moment by external fields taking into consideration the antiferromagnetic interactions. The metamagnetic transition at 36 T originates from crossing of the CEF levels. A scheme for the antiferromagnetic interactions of the U ions, in which the interaction between the 5f spins is mediated by 6d-electron spins, is proposed for U systems. (orig.).

  5. Size effects on the Néel temperature of antiferromagnetic NiO nanoparticles

    Directory of Open Access Journals (Sweden)

    Natalia Rinaldi-Montes

    2016-05-01

    Full Text Available Among all antiferromagnetic transition metal monoxides, NiO presents the highest Néel temperature (TN ∼ 525 K. In this work, the size-dependent reduction of TN in NiO nanoparticles with average diameters (D ranging from 4 to 9 nm is investigated by neutron diffraction. The scaling law followed by TN(D is in agreement with the Binder theory of critical phenomena in low-dimensional systems. X-ray absorption fine structure measurements link the decrease of TN to the occurrence of size effects (average undercoordination, bond relaxation and static disorder in the nearest and next-nearest Ni coordination shells that hold the key for the maintenance of the antiferromagnetic order.

  6. Integration of antiferromagnetic Heusler compound Ru2MnGe into spintronic devices

    Science.gov (United States)

    Balluff, Jan; Huminiuc, Teodor; Meinert, Markus; Hirohata, Atsufumi; Reiss, Günter

    2017-07-01

    We report on the integration of an antiferromagnetic Heusler compound acting as a pinning layer into magnetic tunneling junctions (MTJs). The antiferromagnet Ru2MnGe is used to pin the magnetization direction of a ferromagnetic Fe layer in MgO based thin film tunneling magnetoresistance stacks. The samples were prepared using magnetron co-sputtering. We investigate the structural properties by X-ray diffraction and reflection, as well as atomic force and high-resolution transmission electron microscopy. We find an excellent crystal growth quality with a low interface roughnesses of 1-3 Å, which is crucial for the preparation of working tunneling barriers. Using Fe as a ferromagnetic electrode material, we prepared magnetic tunneling junctions and measured the magnetoresistance. We find a sizeable maximum magnetoresistance value of 135%, which is comparable to other common Fe based MTJ systems.

  7. Easy moment direction and antiferromagnetic domain wall motion in Mn{sub 2}Au

    Energy Technology Data Exchange (ETDEWEB)

    Barthem, Vitoria M.T.S. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Ilha do Fundao, 21941-972 Rio de Janeiro (Brazil); Colin, Claire V.; Haettel, Richard; Dufeu, Didier [Université Grenoble Alpes, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France); CNRS, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France); Givord, Dominique, E-mail: dominique.givord@neel.cnrs.fr [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Ilha do Fundao, 21941-972 Rio de Janeiro (Brazil); Université Grenoble Alpes, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France); CNRS, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France)

    2016-05-15

    The interest of giving active functions to antiferromagnetic (AFM) materials in spintronics devices has been realized recently. Mn{sub 2}Au is a high-Néel temperature antiferromagnet with large Mn moment, lying in plane of the tetragonal structure. To determine the direction of the moments in Mn{sub 2}Au, an original approach is demonstrated, which should be generic to planar AFM materials. It involves the rotation of the granular sample around an axis perpendicular to the applied magnetic field. The family of easy moment directions is 〈110〉. For grains prevented from rotating, the dominant magnetization process is AFM domain wall motion. Textured Mn{sub 2}Au nanoelements could be introduced in spintronics devices, in which the Mn moments would be switched under modest external excitation.

  8. Frustrated ground state in the metallic Ising antiferromagnet Nd2Ni2In

    Science.gov (United States)

    Sala, G.; Mašková, S.; Stone, M. B.

    2017-10-01

    We used inelastic neutron scattering measurements to examine the intermetallic Ising antiferromagnet Nd2Ni2In . The dynamical structure factor displays a spectrum with multiple crystal field excitations. These crystal field excitations consist of a set of four transitions covering a range of energies between 4 and 80 meV. The spectrum is very sensitive to the temperature, and we observed a softening and a shift in the energies above the transition temperature of the system. The analysis of the crystalline electric field scheme confirms the Ising nature of the spins and their orientation as proposed by previous studies. We characterized Nd2Ni2In as a large moment intermetallic antiferromagnet with the potential to support a geometrically frustrated Shastry-Sutherland lattice.

  9. Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films

    KAUST Repository

    Cossu, Fabrizio

    2013-06-21

    Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.

  10. Electric Control of Dirac Quasiparticles by Spin-Orbit Torque in an Antiferromagnet.

    Science.gov (United States)

    Šmejkal, L; Železný, J; Sinova, J; Jungwirth, T

    2017-03-10

    Spin orbitronics and Dirac quasiparticles are two fields of condensed matter physics initiated independently about a decade ago. Here we predict that Dirac quasiparticles can be controlled by the spin-orbit torque reorientation of the Néel vector in an antiferromagnet. Using CuMnAs as an example, we formulate symmetry criteria allowing for the coexistence of topological Dirac quasiparticles and Néel spin-orbit torques. We identify the nonsymmorphic crystal symmetry protection of Dirac band crossings whose on and off switching is mediated by the Néel vector reorientation. We predict that this concept verified by minimal model and density functional calculations in the CuMnAs semimetal antiferromagnet can lead to a topological metal-insulator transition driven by the Néel vector and to the topological anisotropic magnetoresistance.

  11. All-oxide-based synthetic antiferromagnets exhibiting layer-resolved magnetization reversal

    Science.gov (United States)

    Chen, Binbin; Xu, Haoran; Ma, Chao; Mattauch, Stefan; Lan, Da; Jin, Feng; Guo, Zhuang; Wan, Siyuan; Chen, Pingfan; Gao, Guanyin; Chen, Feng; Su, Yixi; Wu, Wenbin

    2017-07-01

    Synthesizing antiferromagnets with correlated oxides has been challenging, owing partly to the markedly degraded ferromagnetism of the magnetic layer at nanoscale thicknesses. Here we report on the engineering of an antiferromagnetic interlayer exchange coupling (AF-IEC) between ultrathin but ferromagnetic La2/3Ca1/3MnO3 layers across an insulating CaRu1/2Ti1/2O3 spacer. The layer-resolved magnetic switching leads to sharp steplike hysteresis loops with magnetization plateaus depending on the repetition number of the stacking bilayers. The magnetization configurations can be switched at moderate fields of hundreds of oersted. Moreover, the AF-IEC can also be realized with an alternative magnetic layer of La2/3Sr1/3MnO3 that possesses a Curie temperature near room temperature. The findings will add functionalities to devices with correlated-oxide interfaces.

  12. Real-space renormalization-group studies of low-dimensional quantum antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Lepetit, M. (Laboratoire de Physique Quantique, Universite Paul Sabatier, 118 route de Narbonne, 31062 Toulouse CEDEX (France)); Manousakis, E. (Department of Physics, Center for Materials Research and Technology Supercomputer Computations Research Isntitute, Florida State University, Tallahassee, Florida 32306 (United States))

    1993-07-01

    We study the ground state of one- and two-dimensional (square-lattice) spin-1/2 quantum antiferromagnets using a numerical real-space renormalization-group (RG) approach. In our RG approach we consider blocks of various sizes but with an odd number of sites; we retain only the doublet ground state and we integrate out the higher-energy states by means of second-order quasidegenerate perturbation theory. That is, we assume that the role of the excited states of a block, in the RG iteration process, is to renormalize the effective coupling parameters between blocks. We compute the ground-state energy of a spin-1/2 linear chain for various block sizes and find close agreement with the Bethe-ansatz exact solution. In the case of the spin-1/2 square-lattice quantum antiferromagnet, the obtained ground-state energy is in reasonable agreement with the available numerical estimates.

  13. Topological stripelike coreless textures with inner incommensurability in two-dimensional Heisenberg antiferromagnet

    OpenAIRE

    Sinitsyn, E. V.; Bostrem, I. G.; Ovchinnikov, A. S.

    2004-01-01

    For two-dimensional Heisenberg antiferromagnet we present an analysis of topological coreless excitations having a stripe form. These textures are characterized by singularities at boundaries. A detailed classification of the stripe textures results in a certain analogy with the coreless excitations in $^3He-A$ phase: Mermin-Ho and Anderson-Toulouse coreless vortices. The excitations of the last type may have a low bulk energy. The stripe textures may be observed as an occurrence of short-ran...

  14. No antiferromagnetic reordering at low temperature in pure YBa2Cu3O6+x

    DEFF Research Database (Denmark)

    Casalta, H.; Schleger, P.; Brecht, E.

    1994-01-01

    Magnetic ordering has been investigated by neutron scattering on an YBa2Cu3O6+x single crystal with x=0.1 and x=0.18, and an Al doped YBa2(CU2.86Al0.14)O-6.25 crystal. For the undoped crystal an antiferromagnetic ordering transition (AFI) was observed at T-N=410 K and 368 K (respectively for x=0...

  15. Spin Structures and Phase Diagrams of Extended Spatially Completely Anisotropic Triangular Lattice Antiferromagnets

    Science.gov (United States)

    Sakakida, Keishiro; Shimahara, Hiroshi

    2017-12-01

    Motivated by recently discovered organic antiferromagnets, we examine an extended triangular lattice that consists of two types of triangles of bonds with exchange coupling constants Jℓ and J'ℓ (ℓ= 1, 2, and 3), respectively. The simplified system with Jℓ = J'ℓ > 0 is the spatially completely anisotropic triangular lattice (SCATL) antiferromagnet examined previously. The extended system, which we call an extended SCATL (ESCATL), has two different spatial anisotropy parameters J3/J2 and J'3/J'2 when J1 = J'1 is assumed. We derive classical phase diagrams and spin structures. It is found that the ESCATL antiferromagnet exhibits two up-up-down-down (uudd) phases when the imbalance of the anisotropy parameters is significant, in addition to the three Néel phases that occur in the SCATL. When the model parameters vary, these collinear phases are continuously connected by the spiral-spin phase. Using the available model parameters for the organic compounds λ-(BETS)2XCl4 (X = Fe and Ga), we examine the stabilities of the spin structures of the independent π-electron system, which is considered to primarily sustain the magnetic order, where BETS represents bis(ethylenedithio)tetraselenafulvalene. It is found that one of the uudd phases has an energy close to the ground-state energy for λ-(BETS)2FeCl4. We discuss the relevance of the magnetic anion FeCl4 and the quantum fluctuation to the magnetism of these compounds. When J'3 = 0, the system is reduced to a trellis lattice antiferromagnet. The system exhibits a stripe spiral-spin phase, which comprises one-dimensional spiral-spin states stacked alternately.

  16. Enhanced exchange bias fields for CoO/Co bilayers: influence of antiferromagnetic grains and mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Cheng-Hsun-Tony; Chang, Shin-Chen [Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan (China); Tsay, Jyh-Shen, E-mail: jstsay@phy.ntnu.edu.tw [Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan (China); Yao, Yeong-Der [Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan (China)

    2017-05-31

    Highlights: • An antiferromagnetic grain model on exchange bias phenomena is proposed. • Grain size and grain density are considered. • For smaller grain size, the dependence of t{sub CoO} on T{sub B} showed a less pronounced variation. • An increased grain density is responsible for the enhancement in the exchange bias fields. - Abstract: The emergence and optimization of devices that can be applied to spintronics have attracted considerable interest, and both experimental and theoretical approaches have been used in studies of exchange bias phenomena. A survey of the literature indicates that great efforts have been devoted to improving exchange bias fields, while only limited attempts have been made to control the temperature dependence of exchange bias. In this study, the influence of antiferromagnetic grains on exchange bias phenomena in CoO/Co bilayers on a semiconductor surface was investigated. Based on an antiferromagnetic grain model, a correlation between grain size, grain density, blocking temperature, and the exchange bias field was established. For crystallites with a smaller median diameter, the dependence of the thickness of the CoO layer on blocking temperature showed a less pronounced variation. This is due to the larger thermal agitation of the atomic spin moments in the grain, which causes a weaker exchange coupling between atomic spin moments. The enhanced density of antiferromagnetic/ferromagnetic pinning sites resulting from an increased grain density is responsible for the enhancement in the exchange bias fields. The results reported herein provide insights into our knowledge related to controlling the temperature dependence of exchange bias and related mechanisms.

  17. Field-Induced Magnetostructural Transitions in Antiferromagnetic Fe1+ y Te1- x S x

    Science.gov (United States)

    Tokunaga, M.; Kihara, T.; Mizuguchi, Y.; Takano, Y.

    2013-03-01

    Transport and structural properties of Fe1+ y Te1- x S x were studied in pulsed magnetic fields. Application of high magnetic fields induces first order transitions showing positive magnetoresistance effects in the antiferromagnetic phase. Polarizing microscope images taken at high magnetic fields revealed the concomitant melting of the orbital order. These results indicate the importance of crossed coupling between spin and lattice or orbital degrees of freedom in this compound.

  18. Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins.

    Science.gov (United States)

    Radu, I; Vahaplar, K; Stamm, C; Kachel, T; Pontius, N; Dürr, H A; Ostler, T A; Barker, J; Evans, R F L; Chantrell, R W; Tsukamoto, A; Itoh, A; Kirilyuk, A; Rasing, Th; Kimel, A V

    2011-04-14

    Ferromagnetic or antiferromagnetic spin ordering is governed by the exchange interaction, the strongest force in magnetism. Understanding spin dynamics in magnetic materials is an issue of crucial importance for progress in information processing and recording technology. Usually the dynamics are studied by observing the collective response of exchange-coupled spins, that is, spin resonances, after an external perturbation by a pulse of magnetic field, current or light. The periods of the corresponding resonances range from one nanosecond for ferromagnets down to one picosecond for antiferromagnets. However, virtually nothing is known about the behaviour of spins in a magnetic material after being excited on a timescale faster than that corresponding to the exchange interaction (10-100 fs), that is, in a non-adiabatic way. Here we use the element-specific technique X-ray magnetic circular dichroism to study spin reversal in GdFeCo that is optically excited on a timescale pertinent to the characteristic time of the exchange interaction between Gd and Fe spins. We unexpectedly find that the ultrafast spin reversal in this material, where spins are coupled antiferromagnetically, occurs by way of a transient ferromagnetic-like state. Following the optical excitation, the net magnetizations of the Gd and Fe sublattices rapidly collapse, switch their direction and rebuild their net magnetic moments at substantially different timescales; the net magnetic moment of the Gd sublattice is found to reverse within 1.5 picoseconds, which is substantially slower than the Fe reversal time of 300 femtoseconds. Consequently, a transient state characterized by a temporary parallel alignment of the net Gd and Fe moments emerges, despite their ground-state antiferromagnetic coupling. These surprising observations, supported by atomistic simulations, provide a concept for the possibility of manipulating magnetic order on the timescale of the exchange interaction.

  19. Hypnotic suggestion and cognitive neuroscience.

    Science.gov (United States)

    Oakley, David A; Halligan, Peter W

    2009-06-01

    The growing acceptance of consciousness as a legitimate field of enquiry and the availability of functional imaging has rekindled research interest in the use of hypnosis and suggestion to manipulate subjective experience and to gain insights into healthy and pathological cognitive functioning. Current research forms two strands. The first comprises studies exploring the cognitive and neural nature of hypnosis itself. The second employs hypnosis to explore known psychological processes using specifically targeted suggestions. An extension of this second approach involves using hypnotic suggestion to create clinically informed analogues of established structural and functional neuropsychological disorders. With functional imaging, this type of experimental neuropsychopathology offers a productive means of investigating brain activity involved in many symptom-based disorders and their related phenomenology.

  20. Carbon-Induced Ferromagnetism in the Antiferromagnetic Metallic Host Material Mn3ZnN.

    Science.gov (United States)

    Sun, Ying; Guo, Yanfeng; Tsujimoto, Yoshihiro; Yang, Jiajia; Shen, Bin; Yi, Wei; Matsushita, Yoshitaka; Wang, Cong; Wang, Xia; Li, Jun; Sathish, Clastin I; Yamaura, Kazunari

    2013-01-18

    Carbon-for-nitrogen substitution (51 at% at most) was achieved in the antiferromagnetic metallic host material Mn(3)ZnN. The various carbon-doped compounds were studied using synchrotron X-ray diffraction, and their electrical resistivities, specific heats, and degrees of magnetization were measured for temperatures of 2-400 K. The sharp antiferromagnetic-to-paramagnetic transition of the host material at 185 K broadened markedly as the carbon content was increased, and a significant ferromagnetic character was found to coexist with the antiferromagnetism when the carbon concentration exceeded 27 at%. This critical magnetic behavior is likely in part due to the increase in the density of states at the Fermi level and the increase in the distance between neighboring Mn atoms. The exact mechanism responsible for the induction of the complicated magnetic state could not be determined. However, the results demonstrate clearly that the chemical tuning of the X site in antiperovskite Mn(3)AX materials is as useful as that of the A and Mn sites and can be used to develop the properties of these materials for practical applications.

  1. Ground states of anisotropic antiferromagnets with single ion and cubic anisotropy

    Directory of Open Access Journals (Sweden)

    T.-C. Dinh

    2009-01-01

    Full Text Available Anisotropic antiferromagnets in an external magnetic field show a rich variety of different ground states meeting in transition lines and multicritical points. We study the dependence of the ground states of these systems in the three dimensional space on physical parameters such as exchange, single ion and cubic anisotropy. One identifies four different ground states: the paramagnetic (PM, the antiferromagnetic (AF, the spin flop (SF and the biconical (BC ground state. In the case of absence of a cubic anisotropy, the transition lines separating different ground states can be calculated analytically, otherwise they have to be calculated numerically. We also considered the behavior of the staggered magnetization which characterizes the different ground states. From its behavior the order of the transition from one state to the other is determined. But also the order of the transition changes along the transition lines when including the cubic anisotropy, especially at the reeentrant region where a transition from SF to BC and back to SF by increasing the external field H occurs. Multicritical points are found which are assumed to be tricritical or critical endpoints. The results obtained may be relevant for other systems since the antiferromagnetic model can be mapped to a lattice gas model where the biconical ground state is interpreted as supersolid phase. Recent renormalization group calculations show that such a phase would indicate the existence of a tetracritical point.

  2. Interconnections between magnetic state and transport currents in antiferromagnetic Sr2IrO4

    Science.gov (United States)

    Tsoi, Maxim

    Interconnections between magnetic state and transport currents in ferromagnetic (F) heterostructures are the basis for spintronic applications, e.g. tunneling magnetoresistance and spin-transfer torque phenomena provide a means to read and write information in magnetic memory devices like STTRAM. Similar interconnections were proposed to occur in systems where F-components are replaced with antiferromagnets (AFM). We demonstrated experimentally the existence of such interconnections in antiferromagnetic Mott insulator Sr2IrO4: first, we found a very large anisotropic magnetoresistance (AMR) which can be used to monitor (read) the magnetic state of AFM; second, we demonstrated the feasibility of reversible resistive switching driven by high-density currents/high electric fields which can be used for writing in AFM memory applications. These results support the feasibility of AFM spintronics where antiferromagnets are used in place of ferromagnets. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, and by NSF grants DMR-1207577, DMR-1265162 and DMR-1122603.

  3. Spin Seebeck effect in the polar antiferromagnet α -Cu2V2O7

    Science.gov (United States)

    Shiomi, Y.; Takashima, R.; Okuyama, D.; Gitgeatpong, G.; Piyawongwatthana, P.; Matan, K.; Sato, T. J.; Saitoh, E.

    2017-11-01

    We have studied the longitudinal spin Seebeck effect in a polar antiferromagnet α -Cu2V2O7 in contact with a Pt film. Below the antiferromagnetic transition temperature of α -Cu2V2O7 , spin Seebeck voltages whose magnetic-field dependence is similar to that reported in antiferromagnetic MnF2|Pt bilayers are observed. Though a small weak-ferromagnetic moment appears owing to the Dzyaloshinskii-Moriya interaction in α -Cu2V2O7 , the magnetic-field dependence of spin Seebeck voltages is found to be irrelevant to the weak-ferromagnetic moments. The dependences of the spin Seebeck voltages on magnetic fields and temperature are analyzed by a magnon spin-current theory. The numerical calculation of spin Seebeck voltages using magnetic parameters of α -Cu2V2O7 determined by previous neutron-scattering studies reveals that the magnetic-field and temperature dependences of the spin Seebeck voltages for α -Cu2V2O7| Pt are governed by the changes in magnon lifetimes with magnetic fields and temperature.

  4. Magnetic transitions under ultrahigh magnetic fields of up to 130 T in the breathing pyrochlore antiferromagnet LiInCr4O8

    Science.gov (United States)

    Okamoto, Yoshihiko; Nakamura, Daisuke; Miyake, Atsushi; Takeyama, Shojiro; Tokunaga, Masashi; Matsuo, Akira; Kindo, Koichi; Hiroi, Zenji

    2017-04-01

    The magnetization processes of the spin-3/2 antiferromagnet LiInCr4O8 comprising a "breathing" pyrochlore lattice, which is an alternating array of small and large tetrahedra, are studied under ultrahigh magnetic fields of up to 130 T using state-of-the-art pulsed magnets. A half magnetization plateau is observed above 90 T to 130 T, suggesting that LiInCr4O8 has a strong spin-lattice coupling, similar to conventional chromium spinel oxides. The magnetization of LiGa0.125In0.875Cr4O8 , in which the structural and magnetic transitions at low temperatures have been completely suppressed, shows a sudden increase above 13 T, indicating that a spin gap of 2.2 meV exists between a tetramer singlet ground state and an excited state with total spin 1, with the latter being stabilized by the application of a magnetic field. The breathing pyrochlore antiferromagnet is found to be a unique frustrated system with strong spin-lattice coupling and bond alternation.

  5. Deepening sleep by hypnotic suggestion.

    OpenAIRE

    Cordi, Maren J.; Schlarb, Angelika A; Rasch, Björn

    2014-01-01

    STUDY OBJECTIVES Slow wave sleep (SWS) plays a critical role in body restoration and promotes brain plasticity; however it markedly declines across the lifespan. Despite its importance effective tools to increase SWS are rare. Here we tested whether a hypnotic suggestion to "sleep deeper" extends the amount of SWS. DESIGN Within subject placebo controlled crossover design. SETTING Sleep laboratory at the University of Zurich Switzerland. PARTICIPANTS Seventy healthy females 23.27 ± 3.17 y. IN...

  6. Interlayer coupling between out-of-plane magnetized multilayers across a thin antiferromagnetic spacer

    Energy Technology Data Exchange (ETDEWEB)

    Moritz, J., E-mail: jerome.moritz@cea.fr [SPINTEC, UMR CEA/CNRS/UJF/Grenoble-INP, Grenoble (France); Bacher, P. [LEMTA, UMR CNRS-INPL-UHP, ESSTIN, 2, rue Jean Lamour, Vandoeuvre Les Nancy Cedex F-54519 (France); Auffret, S.; Dieny, B. [SPINTEC, UMR CEA/CNRS/UJF/Grenoble-INP, Grenoble (France)

    2011-10-15

    The interlayer exchange coupling between Co/Pt perpendicular-to-plane magnetized layers across a thin IrMn spacer layer was experimentally studied. In contrast to earlier studies on interlayer coupling through antiferromagnetic NiO, which revealed an oscillatory coupling behavior as a function of NiO thickness, a ferromagnetic coupling was observed here in the range of IrMn thickness between 0.6 and 1.5 nm and antiferromagnetic between 1.5 and 2.5 nm. The antiferromagnetic coupling is attributed to an orange peel magnetostatic mechanism whereas the ferromagnetic coupling is attributed to an out-of-plane polarization of the antiferromagnetic IrMn layer induced by the interfacial exchange interaction with the adjacent out-of-plane ferromagnetic layers. Measurements of hysteresis loops versus temperature show that the coupling vanishes at 510 K for t{sub IrMn}=1 nm. This critical temperature is far below the Neel temperature of bulk IrMn, but above the blocking temperature of IrMn/Co bilayers at such thickness. Using a one-dimensional model describing a partial domain wall in the antiferromagnet, we explain the coupling in terms of an out-of-plane tilt of the Mn moments at the IrMn/(Co/Pt) interfaces yielding a weak net polarization of the IrMn. Finally, the non-oscillatory decay of the coupling was attributed to the compensated spin structure of the IrMn in the parallel to the interfaces. - Highlights: > Interlayer coupling between Pt/Co multilayer separated by thin IrMn film is studied. > Coupling is ferromagnetic at low thickness of IrMn (between 0.6 and 1.2 nm). > Coupling vanishes between the blocking and the Neel temperature of IrMn. > We model the coupling by considering a tilt of the interfacial IrMn spins. > Non-oscillatory coupling is attributed to the compensated spin structure of IrMn.

  7. Genetic susceptibility of periodontitis

    NARCIS (Netherlands)

    Laine, M.L.; Crielaard, W.; Loos, B.G.

    2012-01-01

    In this systematic review, we explore and summarize the peer-reviewed literature on putative genetic risk factors for susceptibility to aggressive and chronic periodontitis. A comprehensive literature search on the PubMed database was performed using the keywords ‘periodontitis’ or ‘periodontal

  8. Fourie susceptible.pmd

    African Journals Online (AJOL)

    Prof. Adipala Ekwamu

    a number of cultivars exhibited field resistance to halo blight and bacterial brown spot, all cultivars were more or less susceptible to .... Cerillos. Alubia. I. 91. 57. Kranskop. Red speckled sugar. II. 97. 63. OPS-RS1. Red speckled sugar. II. 96. 63. OPS-RS2. Red speckled sugar. I. 100. 61. OPS-RS3. Red speckled sugar. II. 97.

  9. Association analyses suggest GPR24 as a shared susceptibility gene for bipolar affective disorder and schizophrenia

    DEFF Research Database (Denmark)

    Severinsen, J E; Als, T D; Binderup, H

    2006-01-01

    M segment on 22q13. The present study investigated three candidate genes located in this segment: GPR24, ADSL, and ST13. Nine SNPs located in these genes and one microsatellite marker (D22S279) were applied in an association analysis of two samples: an extension of the previously analyzed Faeroese sample...... comprising 28 distantly related cases (17 BPD, 11 SZ subjects) and 44 controls, and a Scottish sample including 162 patients with BPD, 103 with SZ, and 200 controls. In both samples significant associations were observed in both disorders with predominantly GPR24 SNPs and haplotypes. In the Faeroese sample......(-5) and 0.0006 in the combined group of cases from the Faeroe Islands and Scotland, respectively. The G protein-coupled receptor 24 encoded by GPR24 binds melanin-concentrating hormone (MCH) and has been implicated with feeding behavior, energy metabolism, and regulation of stress and mood. To our knowledge...

  10. Spin ordering and dynamics in the frustrated antiferromagnet YBaCo 4 O 7.1

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, S.; Hu, X.; Kuhns, P. L.; Reyes, A. P.; Brooks, J. S.; Besara, T.; Siegrist, T.; Zheng, H.; Mitchell, J. F.; Hoch, M. J. R.

    2014-03-01

    The stoichiometric 114-layered material YBaCo407 exhibits long-range antiferromagnetic order below a Neel temperature of 106 K. Nonstoichiometric YBaCo4O7.1. which contains a relatively small amount (1.4%) of interstitial oxygen, has recently been shown to have drastically modified magnetic properties compared to the parent compound. The present experiments have used magnetization, ac susceptibility, and zero applied field NMR to study the spin configuration and spin dynamics in a single crystal of YBaCo4O7.1 as a function of temperature below 100 K. Evidence has been obtained for a magnetic transition at 80 K corresponding to some form of spin freeze-out. Based on previous results for the stoichiometric material, it is likely that the freezing process involves spins in the triangular layers in this frustrated antiferromagnet. At lower temperatures, dynamic effects persist and below 50 K a fraction of the spins, located primarily in the kagom.e layers, constitute what may be termed a viscous spin liquid component. For T < 10 K, a disordered or glasslike spin structure, with a large distribution of spin correlation times, emerges as the low-temperature state of the spin system.

  11. Genetic Susceptibility to Atherosclerosis

    Directory of Open Access Journals (Sweden)

    Sanja Kovacic

    2012-01-01

    Full Text Available Atherosclerosis is a complex multifocal arterial disease involving interactions of multiple genetic and environmental factors. Advances in techniques of molecular genetics have revealed that genetic ground significantly influences susceptibility to atherosclerotic vascular diseases. Besides further investigations of monogenetic diseases, candidate genes, genetic polymorphisms, and susceptibility loci associated with atherosclerotic diseases have been identified in recent years, and their number is rapidly increasing. This paper discusses main genetic investigations fields associated with human atherosclerotic vascular diseases. The paper concludes with a discussion of the directions and implications of future genetic research in arteriosclerosis with an emphasis on prospective prediction from an early age of individuals who are predisposed to develop premature atherosclerosis as well as to facilitate the discovery of novel drug targets.

  12. acetyltransferases: Influence on Lung Cancer Susceptibility

    African Journals Online (AJOL)

    Lung cancer remains a major health challenge in the world. It is the commonest cause of cancer mortality in men, it has been suggested that genetic susceptibility may contribute to the major risk factor, with increasing prevalence of smoking. Lung cancer has reached epidemic proportions in India. Recently indoor air ...

  13. Marijuana Usage and Hypnotic Susceptibility

    Science.gov (United States)

    Franzini, Louis R.; McDonald, Roy D.

    1973-01-01

    Anonymous self-reported drug usage data and hypnotic susceptibility scores were obtained from 282 college students. Frequent marijuana users (more than 10 times) showed greater susceptibility to hypnosis than nonusers. (Author)

  14. Optical determination of the Néel vector in a CuMnAs thin-film antiferromagnet

    Science.gov (United States)

    Saidl, V.; Němec, P.; Wadley, P.; Hills, V.; Campion, R. P.; Novák, V.; Edmonds, K. W.; Maccherozzi, F.; Dhesi, S. S.; Gallagher, B. L.; Trojánek, F.; Kuneš, J.; Železný, J.; Malý, P.; Jungwirth, T.

    2017-01-01

    Recent breakthroughs in the electrical detection and manipulation of antiferromagnets have opened a new avenue in the research of non-volatile spintronic devices. Antiparallel spin sublattices in antiferromagnets, producing zero dipolar fields, lead to insensitivity to magnetic field perturbations, multi-level stability, ultrafast spin dynamics and other favourable characteristics, and may find utility in fields ranging from magnetic memories to optical signal processing. However, the absence of a net magnetic moment and ultrashort magnetization dynamics timescales make antiferromagnets notoriously difficult to study using common magnetometers or magnetic resonance techniques. Here, we demonstrate the experimental determination of the Néel vector in a thin film of antiferromagnetic CuMnAs (refs 9,10), a prominent material used in the first realization of antiferromagnetic memory chips. We use a table-top femtosecond pump-probe magneto-optical experiment that is considerably more accessible than the traditionally employed large-scale-facility techniques such as neutron diffraction and X-ray magnetic dichroism measurements.

  15. Cluster algorithms for frustrated two-dimensional Ising antiferromagnets via dual worm constructions

    Science.gov (United States)

    Rakala, Geet; Damle, Kedar

    2017-08-01

    We report on the development of two dual worm constructions that lead to cluster algorithms for efficient and ergodic Monte Carlo simulations of frustrated Ising models with arbitrary two-spin interactions that extend up to third-neighbors on the triangular lattice. One of these algorithms generalizes readily to other frustrated systems, such as Ising antiferromagnets on the Kagome lattice with further neighbor couplings. We characterize the performance of both these algorithms in a challenging regime with power-law correlations at finite wave vector.

  16. Antiferromagnetic Nd ordering in NdPd{sub 2}Ga{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Doenni, A.; Fischer, P.; Fauth, F.; Zolliker, M. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Bauer, E. [Technische Univ., Vienna (Austria)

    1997-09-01

    The ternary intermetallic compound NdPd{sub 2}Ga{sub 3} was investigated by powder neutron diffraction: the crystal structure agrees well with the ordered hexagonal PrNi{sub 2}Al{sub 3}-type structure. The antiferromagnetic ordering below T{sub N} 6.5 K corresponds to a propagation vector k = [1/2,0,0]. The ordered magnetic Nd moments of (1.99 {+-} 0.04) {mu}{sub B} at saturation lie in the basal plane due to the crystal-electric field anisotropy and are oriented perpendicular to the propagation vector. (author) 1 fig., 1 tab., 2 refs.

  17. Tunable magnetic anisotropy of antiferromagnetic superlattice and resultant exchange bias of ferromagnetic layer on it

    Energy Technology Data Exchange (ETDEWEB)

    Tsunoda, Masakiyo [Department of Electonic Engineering, Tohoku University, Aobayama 6-6-05, Sendai 980-8579 (Japan)]. E-mail: tsunoda@ecei.tohoku.ac.jp; Naka, Mamiko [Department of Electonic Engineering, Tohoku University, Aobayama 6-6-05, Sendai 980-8579 (Japan); Kim, Dong Young [Department of Electonic Engineering, Tohoku University, Aobayama 6-6-05, Sendai 980-8579 (Japan); Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Takahashi, Migaku [Department of Electonic Engineering, Tohoku University, Aobayama 6-6-05, Sendai 980-8579 (Japan); New Industry Creation Hatchery Center, Tohoku University, Aobayama 6-6-10, Sendai 980-8579 (Japan)

    2006-09-15

    Exchange biasing of ferromagnetic layer deposited on the antiferromagnetic superlattice was investigated in (Co{sub 70}Fe{sub 30}/Ru){sub 29.5}/Ru/Co{sub 90}Fe{sub 10} multilayers. Uniaxial magnetic anisotropy (K {sub AF}) was induced and tuned in the antiferromagentic superlattice by uniaxial substrate bending method through the inverse effect of magnetostriction. The exchange bias increased and tended to be saturated with increasing the K {sub AF}, while it was not observed at K {sub AF}=0.

  18. Large exchange-dominated domain wall velocities in antiferromagnetically coupled nanowires

    Directory of Open Access Journals (Sweden)

    Majd Kuteifan

    2016-04-01

    Full Text Available Magnetic nanowires supporting field- and current-driven domain wall motion are envisioned for methods of information storage and processing. A major obstacle for their practical use is the domain-wall velocity, which is traditionally limited for low fields and currents due to the Walker breakdown occurring when the driving component reaches a critical threshold value. We show through numerical and analytical modeling that the Walker breakdown limit can be extended or completely eliminated in antiferromagnetically coupled magnetic nanowires. These coupled nanowires allow for large domain-wall velocities driven by field and/or current as compared to conventional nanowires.

  19. Entanglement in the quantum one-dimensional integer spin S Heisenberg antiferromagnet

    Science.gov (United States)

    Lima, L. S.

    2017-10-01

    We use the modified spin wave theory of Takahashi to study the entanglement entropy in the quantum one-dimensional integer spin Heisenberg antiferromagnet. We calculate the entanglement entropy of this spin system that is well known to be a quantum wire, in the classical limit (N → ∞). We obtain a decreasing the entanglement entropy with the temperature and we obtain none change in the entanglement in the point Δ = 1 at T = 0 where the system presents a quantum phase transition from a gapless phase in the spectrum Δ < 1 to a gapped phase Δ ≥ 1.

  20. μ+SR study of two-dimensional antiferromagnets, delafossite-type compounds

    Science.gov (United States)

    Mekata, M.; Yaguchi, N.; Kuriyama, H.; Asano, T.; Nagamine, K.; Keren, A.; Le, L. P.; Luke, G. M.; Wu, W. D.; Uemura, Y. J.

    1993-03-01

    μ+SR experiments were performed on delafossite-type compounds, CuCrO2, AgCrO2, CuFeO2, which are model compounds of triangular lattice antiferromagnets. The initial asymmetries are much smaller than the expected value, implying muonium formation. The time spectra are composed of slow andfast relaxation components. We attributed the components to signals from μ+ stopped at the center of O2- ions andmuonium far from nuclear dipole moments, respectively. The asymmetries decrease below T N but no precession spectra were observed. Relaxation rates of slow andfast relaxation components show maxima at T N.

  1. Quantum Heisenberg antiferromagnetic chains with exchange and single-ion anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Peters, D; Selke, W [Institut fuer Theoretische Physik, RWTH Aachen University and JARA-SIM, 52056 Aachen (Germany); McCulloch, I P, E-mail: selke@physik.rwth-aachen.d [Department of Physics, University of Queensland, Brisbane, QLD 4072 (Australia)

    2010-01-01

    Using density matrix renormalization group calculations, ground state properties of the spin-1 Heisenberg chain with exchange and quadratic single-ion anisotropies in an external field are studied, for special choices of the two kinds of anisotropies. In particular, the phase diagram includes antiferromagnetic, spin-liquid (or spin-flop), IS2, and supersolid (or biconical) phases. Especially, new features of the spin-liquid and supersolid phases are discussed. Properties of the quantum chains are compared to those of corresponding classical spin chains.

  2. Cluster algorithms for frustrated two-dimensional Ising antiferromagnets via dual worm constructions.

    Science.gov (United States)

    Rakala, Geet; Damle, Kedar

    2017-08-01

    We report on the development of two dual worm constructions that lead to cluster algorithms for efficient and ergodic Monte Carlo simulations of frustrated Ising models with arbitrary two-spin interactions that extend up to third-neighbors on the triangular lattice. One of these algorithms generalizes readily to other frustrated systems, such as Ising antiferromagnets on the Kagome lattice with further neighbor couplings. We characterize the performance of both these algorithms in a challenging regime with power-law correlations at finite wave vector.

  3. Oxygen-induced immediate onset of the antiferromagnetic stacking in thin Cr films on Fe(001)

    Energy Technology Data Exchange (ETDEWEB)

    Berti, Giulia, E-mail: giulia.berti@polimi.it; Brambilla, Alberto; Calloni, Alberto; Bussetti, Gianlorenzo; Finazzi, Marco; Duò, Lamberto; Ciccacci, Franco [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy)

    2015-04-20

    We investigated the magnetic coupling of ultra-thin Cr films grown at 600 K on a Fe(001)-p(1 × 1)O substrate by means of spin-polarized photoemission spectroscopy. Our findings show that the expected antiferromagnetic stacking of the magnetization in Cr(001) layers occurs right from the first atomic layer at the Cr/Fe interface. This is at variance with all previous observations in similar systems, prepared in oxygen-free conditions, which always reported on a delayed onset of the magnetic oscillations due to the occurrence of significant chemical alloying at the interface, which is substantially absent in our preparation.

  4. Strong Coupling of Microwave Photons to Antiferromagnetic Fluctuations in an Organic Magnet

    Science.gov (United States)

    Mergenthaler, Matthias; Liu, Junjie; Le Roy, Jennifer J.; Ares, Natalia; Thompson, Amber L.; Bogani, Lapo; Luis, Fernando; Blundell, Stephen J.; Lancaster, Tom; Ardavan, Arzhang; Briggs, G. Andrew D.; Leek, Peter J.; Laird, Edward A.

    2017-10-01

    Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.

  5. Antiferromagnetic transition in EuCu sub 2 Ge sub 2 single crystals

    CERN Document Server

    Hossain, Z; Yuan, H Q; Sparn, G

    2003-01-01

    Single crystals of EuCu sub 2 Ge sub 2 were grown and characterized using electrical resistivity, magnetization, specific heat and magnetoresistance measurements. The crystals exhibit antiferromagnetic transitions at T sub N sub 1 = 9 K and T sub N sub 2 = 5 K. The T sub N of the flux-grown single crystals reported here are lower than that reported for the polycrystalline sample (T sub N = 13 K) in the literature (Felner and Nowik 1978 J. Phys. Chem. Solids 39 763). The magnetoresistance is positive in the ordered state and negative in the paramagnetic state. The magnetic order could not be suppressed up to a pressure of 25 kbar.

  6. Two-loop free energy of three-dimensional antiferromagnets in external magnetic and staggered fields

    Science.gov (United States)

    Brauner, Tomáš; Hofmann, Christoph P.

    2017-11-01

    Using a model-independent low-energy effective field theory, we calculate the free energy of three-dimensional antiferromagnets in a combination of mutually perpendicular external magnetic and staggered fields at the next-to-next-to-leading, two-loop order. Renormalization is carried out analytically, and the renormalization group invariance of the result is checked explicitly. The free energy is thus expressed solely in terms of temperature, the external fields, and a set of low-energy coupling constants, to be determined by experiment or by matching to the microscopic model of a given concrete material.

  7. Quantum crystal growing: adiabatic preparation of a bosonic antiferromagnet in the presence of a parabolic inhomogeneity

    DEFF Research Database (Denmark)

    Gammelmark, Søren; Eckardt, André

    2013-01-01

    We theoretically study the adiabatic preparation of an antiferromagnetic phase in a mixed Mott insulator of two bosonic atom species in a one-dimensional optical lattice. In such a system one can engineer a tunable parabolic inhomogeneity by controlling the difference of the trapping potentials f...... that during the preparation finite size effects will play a crucial role for a system of realistic size. The experiment that we propose can be realized, for example, using atomic mixtures of rubidium 87 with potassium 41, or ytterbium 168 with ytterbium 174....

  8. Emergent Power-Law Phase in the 2D Heisenberg Windmill Antiferromagnet: A Computational Experiment

    Science.gov (United States)

    Jeevanesan, Bhilahari; Chandra, Premala; Coleman, Piers; Orth, Peter P.

    2015-10-01

    In an extensive computational experiment, we test Polyakov's conjecture that under certain circumstances an isotropic Heisenberg model can develop algebraic spin correlations. We demonstrate the emergence of a multispin U(1) order parameter in a Heisenberg antiferromagnet on interpenetrating honeycomb and triangular lattices. The correlations of this relative phase angle are observed to decay algebraically at intermediate temperatures in an extended critical phase. Using finite-size scaling we show that both phase transitions are of the Berezinskii-Kosterlitz-Thouless type, and at lower temperatures we find long-range Z6 order.

  9. Magnetization Process and Adiabatic Demagnetization of the Antiferromagnetic Spin-1/2 Heisenberg Cubic Cluster

    OpenAIRE

    Strecka, Jozef; Cisarova, Jana

    2013-01-01

    A full energy spectrum of the spin-1/2 Heisenberg cubic cluster is used to investigate a low-temperature magnetization process and adiabatic demagnetization of this zero-dimensional 2x2x2 quantum spin system. It is shown that the antiferromagnetic spin-1/2 Heisenberg cube exhibits at low enough temperatures a stepwise magnetization curve with four intermediate plateaux at zero, one quarter, one half, and three quarters of the saturation magnetization. We have also found the enhanced magnetoca...

  10. Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice.

    Science.gov (United States)

    Aoyama, Kazushi; Kawamura, Hikaru

    2016-06-24

    Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2,1/2,1/2) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.

  11. Initialization of unidirectional anisotropy in a ferromagnet antiferromagnet bilayer by keV-He ion bombardment

    Science.gov (United States)

    Engel, D.; Ehresmann, A.; Schmalhorst, J.; Sacher, M.; Höink, V.; Reiss, G.

    2005-06-01

    A polycrystalline Cu/Ni80Fe20/Mn83Ir17/Co/AlOx ferromagnet-antiferromagnet layer system grown without applying an external magnetic field shows no unidirectional anisotropy in the as-prepared state. After 10 keV-He ion bombardment in an external in-plane magnetic field, a clear unidirectional anisotropy collinear to the magnetic field direction during bombardment is observed, indicating that ion bombardment can be used for this system to initialize the unidirectional exchange anisotropy. The magnetization reversal processes for various ion doses are discussed, based on longitudinal magnetooptical Kerr-effect measurements.

  12. Spin dynamics in the stripe-ordered buckled honeycomb lattice antiferromagnet Ba2NiTeO6

    Energy Technology Data Exchange (ETDEWEB)

    Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; Ono, Toshio; Garlea, Vasile Ovidiu; Winn, Barry L.; Masuda, Takatsugu

    2017-09-01

    We carried out inelastic neutron scattering experiments on a buckled honeycomb lattice antiferromagnet Ba2NiTeO6 exhibiting a stripe structure at a low temperature. Magnetic excitations are observed in the energy range of ℏω≲10 meV having an anisotropy gap of 2 meV at 2 K. We perform spin-wave calculations to identify the spin model. The obtained microscopic parameters are consistent with the location of the stripe structure in the classical phase diagram. Furthermore, the Weiss temperature independently estimated from a bulk magnetic susceptibility is consistent with the microscopic parameters. The results reveal that a competition between the nearest-neighbor and next-nearest-neighbor interactions that together with a relatively large single-ion magnetic anisotropy stabilize the stripe magnetic structure.

  13. Unusual ferromagnetic critical behavior owing to short-range antiferromagnetic correlations in antiperovskite Cu1-xNMn3+x (0.1 <= x <= 0.4)

    Science.gov (United States)

    Lin, Jianchao; Tong, Peng; Cui, Dapeng; Yang, Cheng; Yang, Jie; Lin, Shuai; Wang, Bosen; Tong, Wei; Zhang, Lei; Zou, Youming; Sun, Yuping

    2015-01-01

    For ferromagnets, varying from simple metals to strongly correlated oxides,the critical behaviors near the Curie temperature (TC) can be grouped into several universal classes. In this paper, we report an unusual critical behavior in manganese nitrides Cu1-xNMn3+x (0.1 <= x <= 0.4). Although the critical behavior below TC can be well described by mean field (MF) theory, robust critical fluctuations beyond the expectations of any universal classes are observed above TC in x = 0.1. The critical fluctuations become weaker when x increases, and the MF-like critical behavior is finally restored at x = 0.4. In addition, the paramagnetic susceptibility of all the samples deviates from the Curie-Weiss (CW) law just above TC. This deviation is gradually smeared as x increases. The short-range antiferromagnetic ordering above TC revealed by our electron spin resonance measurement explains both the unusual critical behavior and the breakdown of the CW law.

  14. Magnetic properties of tapiolite (FeTa{sub 2}O{sub 6}); a quasi two-dimensional (2D) antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Chung, E M L [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Lees, M R [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); McIntyre, G J [Institut Laue Langevin, BP 156, 38042, Grenoble Cedex 9 (France); Wilkinson, C [Institut Laue Langevin, BP 156, 38042, Grenoble Cedex 9 (France); Balakrishnan, G [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Hague, J P [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Visser, D [Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 OQX (United Kingdom); Paul, D McK [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2004-11-03

    The possibilities of two-dimensional (2D) short-range magnetic correlations and frustration effects in the mineral tapiolite are investigated using bulk-property measurements and neutron Laue diffraction. In this study of the magnetic properties of synthetic single-crystals of tapiolite, we find that single crystals of FeTa{sub 2}O{sub 6} order antiferromagnetically at T{sub N} = 7.95 {+-} 0.05 K, with extensive two-dimensional correlations existing up to at least 40 K. Although we find no evidence that FeTa{sub 2}O{sub 6} is magnetically frustrated, hallmarks of two-dimensional magnetism observed in our single-crystal data include: (i) broadening of the susceptibility maximum due to short-range correlations (ii) a spin-flop transition and (iii) lambda anomalies in the heat capacity and d({chi}T)/dT. Complementary neutron Laue diffraction measurements reveal 1D magnetic diffuse scattering extending along the c* direction perpendicular to the magnetic planes. This magnetic diffuse scattering, observed for the first time using the neutron Laue technique by VIVALDI, arises directly as a result of 2D short-range spin correlations.

  15. Genetic susceptibility to environmental toxicants

    DEFF Research Database (Denmark)

    2001-01-01

    The toxicological challenges to the chemical industry have in recent years been greatly affected by the rapid innovation and development of analytical, molecular and genetic technologies. ECETOC recognises the importance of developing the technical and intellectual skill bases in academia...... and industrial based laboratories to meet the rapid development of the science base of toxicology. As the technology to determine genetic susceptibility develops, so scientist will be able to describe altered gene expression provoked by chemicals long before they are able to offer valid interpretations...... of their meaning. A potential for inadvertently raising concerns over the effect of chemicals in experimental animals or man, or even the intentional misrepresentation of results to suggest chemicals are “playing” with our genes is enormous. History has shown that some individuals and groups in society are willing...

  16. Antiferromagnetic interlayer coupling and thus induced distinct spin texture for the [LaMnO3/LaCoO3]5 superlattices.

    Science.gov (United States)

    Zhang, Jing; Zhang, Hongrui; Zhang, Xuejing; Guan, Xiangxiang; Shen, Xi; Hong, Deshun; Zhang, Hui; Liu, Banggui; Yu, Richeng; Shen, Baogen; Sun, Jirong

    2017-03-09

    Artificial engineering of an interfacial spin structure of complex oxides with strongly coupled spin, orbital, charge and lattice degrees of freedom is crucially important for the exploration of novel effects associated with magnetic tunneling, exchange biasing, and spin injecting/manipulating, which are the central issues of spintronics. Here we demonstrate the presence of a distinct interlayer coupling between LaMnO3 (LMO) and LaCoO3 (LCO) and the resulting dramatic effect on the spin structure. We found that the LCO layer in (LMO/LCO)5 superlattices exhibits not only an antiferromagnetic coupling with a neighboring LMO layer but also a long-range magnetic order with substantially reduced magnetization. As suggested by density functional theory calculations, interlayer coupling can induce a spatial oscillation of magnetic moment within the LCO layer, resulting in low magnetization.

  17. Antiferromagnetism in Ce1-xLaxAl2Ga2 and Ce1-yYyAl2Ga2 Kondo-lattice systems

    Science.gov (United States)

    Garde, C. S.; Ray, J.; Chandra, G.

    1991-02-01

    We report here resistivity ρ and thermoelectric-power S measurements between 1.7 and 300 K on Ce1-xLaxAl2Ga2 and Ce1-yYyAl2Ga2 Kondo-lattice alloys. By variation of x and y, there is a clear evolution of the Kondo-like resistivity minimum, which is not seen in the parent alloy (x=0). With both La and Y substitutions, the antiferromagnetic transition temperature TN is found to be depressed. It is suggested that this depression by a variation of x can be explained solely on the basis of the weakening of the intersite Ruderman-Kittel-Kasuya-Yosida interaction, whereas with a variation of y, the TN depression results from an interplay of both single-site and intersite effects.

  18. The role of 3d electrons in the appearance of ferromagnetism in the antiferromagnetic Ru2MnGe Heusler compound: a magnetic Compton scattering study.

    Science.gov (United States)

    Mizusaki, S; Ohnishi, T; Douzono, A; Hirose, M; Nagata, Y; Itou, M; Sakurai, Y; Ozawa, T C; Samata, H; Noro, Y

    2012-06-27

    The antiferromagnetism in Ru(2)MnGe can be suppressed by the substitution of V by Mn and ferromagnetism appears. Synchrotron-based magnetic Compton scattering experiments are used in order to investigates the role of 3d electrons in the indirect/direct exchange interactions for the appearance of ferromagnetism. A small spin moment for the itinerant electron part on the magnetic Compton profile indicates that the metallic ferromagnet Ru(2)Mn(0.5)V(0.5)Ge has a weak indirect exchange interaction between the d-like and sp-like (itinerant) electrons. This suggests that the appearance of ferromagnetism is caused by the enhancement of the direct exchange interactions between d-d electrons in the Ru(2)MnGe Heusler compound. These findings indicate that the indirect exchange interaction between itinerant electrons and localized electrons is a significant key point for the appearance of ferromagnetism in this system.

  19. Semiconducting antiferromagnetism in MgH2 doped with 3d transition metals: A first-principles view

    Science.gov (United States)

    Lu, Yi-Lin; Dong, Shengjie; Zhou, Wei; Liu, Yanyu; Zhao, Hui; Wu, Ping

    2017-11-01

    The effects of 3d transition metals V, Cr, Mn, Fe, Co, and Ni doping on the structural, electronic, and magnetic properties of MgH2 were investigated based on density functional calculations. The results indicated that doping such an isolated foreign atom can produce considerable spin polarization and tailor MgH2 into n-type magnetic semiconductor. In particular, the long-range antiferromagnetic coupling was achieved in the Mn, Fe, Co, and Ni doped cases. The stability of the antiferromagnetic phase is mainly due to the hole number and the larger superexchange interaction between the occupied and unoccupied eg (t2g) states. This work pointed out the possibilities of achieving antiferromagnetic characteristic and semiconducting feature in MgH2 upon transition-metal doping for potential application in spintronics and hydride electronics.

  20. Design of L21-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT + GW study

    Science.gov (United States)

    Tas, M.; Şaşıoǧlu, E.; Friedrich, C.; Blügel, S.; Galanakis, I.

    2017-02-01

    Antiferromagnetic spintronics is an on-going growing field of research. Employing both standard density functional theory and the GW approximation within the framework of the full-potential linearized augmented-plane-wave method, we study the electronic and magnetic properties of seven potential antiferromagnetic semiconducting Heusler compounds with 18 (or 28 when Zn is present) valence electrons per unit cell. We show that in these compounds G-type antiferromagnetism is the ground state and that they are all either semiconductors (Cr2ScP, Cr2TiZn, V2ScP, V2TiSi, and V3Al) or semimetals (Mn2MgZn and Mn2NaAl). The many-body corrections have a minimal effect on the electronic band structure with respect to the standard electronic structure calculations.

  1. Nearly Deconfined Spinon Excitations in the Square-Lattice Spin-1/2 Heisenberg Antiferromagnet

    Directory of Open Access Journals (Sweden)

    Hui Shao

    2017-12-01

    Full Text Available We study the spin-excitation spectrum (dynamic structure factor of the spin-1/2 square-lattice Heisenberg antiferromagnet and an extended model (the J-Q model including four-spin interactions Q in addition to the Heisenberg exchange J. Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte Carlo simulations, we can treat the sharp (δ-function contribution to the structure factor expected from spin-wave (magnon excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on Cu(DCOO_{2}·4D_{2}O, where a broad spectral-weight continuum at wave vector q=(π,0 was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. Our results at (π,0 show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at q=(π/2,π/2 (as also seen experimentally. We further investigate the reasons for the small magnon weight at (π,0 and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J-Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret the picture of deconfined spinons at (π,0 in the experiments as nearly deconfined spinons—a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile (π,0-magnon pole in the Heisenberg model and its depletion in the J-Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in

  2. Antiferromagnetic Mott insulating state in the single-component molecular material Pd(tmdt)2

    Science.gov (United States)

    Takagi, Rina; Sari, Dita Puspita; Mohd-Tajudin, Saidah Sakinah; Ashi, Retno; Watanabe, Isao; Ishibashi, Shoji; Miyagawa, Kazuya; Ogura, Satomi; Zhou, Biao; Kobayashi, Akiko; Kanoda, Kazushi

    2017-12-01

    A family of compounds built by a single molecular species, M (tmdt) 2, with a metal ion, M , and organic ligands, tmdt, affords diverse electronic phases due to M -dependent interplays between d electrons in M , and π electrons in tmdt. We investigated the spin state in Pd (tmdt) 2 , a π -electron system without a d -electron contribution, through 1H nuclear magnetic resonance (NMR) and muon-spin resonance experiments. The temperature profiles of the NMR linewidth, relaxation rate, and asymmetry parameter in muon decay show an inhomogeneous antiferromagnetic order with moments distributed around ˜0.1 μB that onsets at above 100 K. This result provides an example of the antiferromagnetic order in a pure π -electron system in M (tmdt) 2, and it demonstrates that correlation among the π electrons is so strong as to give the Néel temperature over 100 K. The small and inhomogeneous moments are understandable as the crucial disorder effect in correlated electrons situated near the Mott transition.

  3. Interplay of antiferromagnetism and superconductivity in cuprates with impurity effect and d-wave pairing

    Energy Technology Data Exchange (ETDEWEB)

    Mohapatra, Rasmita, E-mail: rmrmmohapatra@gmail.com [P.G. Department of Applied Physics and Ballistics, F.M. University, Balasore, Odisha 756019 (India); Rout, G.C., E-mail: gcr@iopb.res.in [Physics Enclave, Plot no-664/4825, Lane-4A, Shree Vihar, Patia, Bhubaneswar, Odisha 751024 (India)

    2015-05-15

    Highlights: • We considered here the interplay of antiferromagnetism (AFM) and Superconductivity (SC) with d-wave pairing symmetry in presence of impurity effect. • The tunneling conductance explains the multiple peaks and dip-hump structure. • It is observed that AFM coupling enhances the superconducting transition temperature. • The low temperature specific heat anomaly due to impurity atoms. - Abstract: We present here a model Hamiltonian to study the interplay between staggered magnetic field and the superconductivity with d-wave pairing symmetry in presence of hybridization between impurity f-electrons of rare-earth ions and 3d-electrons of copper ions. The staggered field and superconducting (SC) gaps are calculated by Green’s function technique and solved self-consistently. The coupling constants are compared using s-wave and d-wave pairings. The strength of hybridization suppresses the magnitude of the gaps; while antiferromagnetic coupling enhances the superconducting transition temperature, but suppresses the Neel temperature. The density of states (DOS) representing tunneling conductance shows complex character with impurity level lying at the Fermi level. The electronic specific heat explains prototype heavy fermion behavior in cuprate systems at low temperatures.

  4. Excitation-Gap Scaling near Quantum Critical Three-Dimensional Antiferromagnets

    Science.gov (United States)

    Lohöfer, M.; Wessel, S.

    2017-04-01

    By means of large-scale quantum Monte Carlo simulations, we examine the quantum critical scaling of the magnetic excitation gap (the triplon gap) in a three-dimensional dimerized quantum antiferromagnet, the bicubic lattice, and identify characteristic multiplicative logarithmic scaling corrections atop the leading mean-field behavior. These findings are in accord with field-theoretical predictions that are based on an effective description of the quantum critical system in terms of an asymptotically free field theory, which exhibits a logarithmic decay of the renormalized interaction strength upon approaching the quantum critical point. Furthermore, using bond-based singlet spectroscopy, we identify the amplitude (Higgs) mode resonance within the antiferromagnetic region. We find a Higgs mass scaling in accord with field-theoretical predictions that relate it by a factor of √{2 } to the corresponding triplon gap in the quantum disordered regime. In contrast to the situation in lower-dimensional systems, we observe in this three-dimensional coupled-dimer system a distinct signal from the amplitude mode also in the dynamical spin structure factor. Its width is observed to vanish proportional to the Higgs mass in the accessible proximity to the quantum critical point.

  5. Indirect RIXS study of bimagnon excitations in triangular-lattice quantum Heisenberg antiferromagnet

    Science.gov (United States)

    Datta, Trinanjan; Luo, Cheng; Huang, Zengye; Yao, Dao-Xin

    2015-03-01

    Bimagnon correlations in triangular-lattice quantum Heisenberg antiferromagnet can be probed by the resonant inelastic X-ray scattering (RIXS) technique. Utilizing an interacting spin wave theory within the Bethe-Salpeter approximation scheme, we compute the K-edge indirect RIXS spectra for the nearest neighbor Heisenberg model with a general S for the entire magnetic brillouin zone. The non-collinear spin arrangement in the triangular lattice geometry supports the intrinsic spontaneous single-magnon decay or recombination. Based on our calculation, we find that the RIXS spectra display a peak at the antiferromagnetic wave vector (4 π / 3 , 0) corresponding to the triangular lattice, which is in contrast to the square lattice case. The major contribution to the RIXS spectra originates from the decay vertices arising from the three-magnon interaction terms, with the quartic interaction contributions subdued. Our results indicate that the spontaneous decay and recombination of magnons inherent to the triangular lattice model can be oberved in the RIXS spectra without a disintegration. GRU Small Grants Program, NBRPC-2012CB821400,NSFC-11275279.

  6. Critical space-time networks and geometric phase transitions from frustrated edge antiferromagnetism.

    Science.gov (United States)

    Trugenberger, Carlo A

    2015-12-01

    Recently I proposed a simple dynamical network model for discrete space-time that self-organizes as a graph with Hausdorff dimension d(H)=4. The model has a geometric quantum phase transition with disorder parameter (d(H)-d(s)), where d(s) is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean-field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.

  7. de Haas-van Alphen measurements on the antiferromagnet URhIn5

    Science.gov (United States)

    Yu, Jing Fei; Bartha, Attila; Custers, Jeroen; Julian, Stephen R.

    2017-09-01

    We report on the results of a de Haas-van Alphen (dHvA) measurement performed on the recently discovered antiferromagnet URhIn5 (TN=98 K), a 5 f analog of the well studied heavy fermion antiferromagnet CeRhIn5. We observe two small Fermi surfaces: a roughly spherical pocket β , with Fβ≃0.3 kT, and a pillow-shaped closed surface, α , with Fα≃1.1 kT. In addition, we observe two higher frequencies γ1 with Fγ1≃3.2 kT and γ2 with Fγ 2≃3.5 kT that are seen only near the c axis, and that may arise on cylindrical Fermi surfaces. The measured cyclotron masses range from 1.9 me to 4.3 me . A simple LDA+SO calculation performed for the paramagnetic ground state shows a very different Fermi surface topology, demonstrating a need for more advanced electronic structure calculations.

  8. Sudden and Slow Quenches into the Antiferromagnetic Phase of Ultracold Fermions

    Science.gov (United States)

    Ojekhile, Monika; Höppner, Robert; Moritz, Henning; Mathey, Ludwig

    2016-12-01

    We propose a method to reach the antiferromagnetic state of two-dimensional Fermi gases trapped in optical lattices: Independent subsystems are prepared in suitable initial states and then connected by a sudden or slow quench of the tunneling between the subsystems. Examples of suitable low-entropy subsystems are double wells or plaquettes, which can be experimentally realised in Mott insulating shells using optical super-lattices. We estimate the effective temperature T* of the system after the quench by calculating the distribution of excitations created using the spin wave approximation in a Heisenberg model. We investigate the effect of an initial staggered magnetic field and find that for an optimal polarisation of the initial state the effective temperature can be significantly reduced from T*≈1.7 Tc at zero polarisation to T*<0.65Tc, where Tc is the crossover temperature to the antiferromagnetic state. The temperature can be further reduced using a finite quench time. We also show that T* decreases logarithmically with the linear size of the subsystem.

  9. Ising, heisenberg and hubbard models in relation to insulating and metallic ferro- and antiferro-magnets

    Science.gov (United States)

    March, N. H.; Klein, D. J.

    The Ising model in low dimensions is used for ferromagnets to relate internal energy and entropy to the magnetization. While this is done throughout the ferromagnetic phase, the low temperature predictions are compared with microscopic elementary excitations theory for both insulating and metallic ferromagnets. The model predictions are oversimplified. The spin s=1/2 Heisenberg model for an insulating antiferromagnet is then considered, starting from one dimension and building up a two-dimensional square lattice from lattice strips of variable width. Chemical approaches based an counting local spin-pairing patterns (or Kekulé structures) are brought into contact with recent work on ladders, with both even and odd numbers of legs, in the context of high-T c cuprates. Finally, the Hubbard model and the closely related t-J model are discussed. For the former, simple rules, again based on a chemical approach, are proposed for predicting the spin properties of the ground states and comparison is made with existing computer studies. The related t-J model is briefly considered in relation to carriers moving through antiferromagnetic assemblies as in the high-T c materials.

  10. Superconductivity, charge-density waves, antiferromagnetism, and phase separation in the Hubbard-Holstein model

    Science.gov (United States)

    Karakuzu, Seher; Tocchio, Luca F.; Sorella, Sandro; Becca, Federico

    2017-11-01

    By using variational wave functions and quantum Monte Carlo techniques, we investigate the interplay between electron-electron and electron-phonon interactions in the two-dimensional Hubbard-Holstein model. Here, the ground-state phase diagram is triggered by several energy scales, i.e., the electron hopping t , the on-site electron-electron interaction U , the phonon energy ω0, and the electron-phonon coupling g . At half filling, the ground state is an antiferromagnetic insulator for U ≳2 g2/ω0 , while it is a charge-density-wave (or bipolaronic) insulator for U ≲2 g2/ω0 . In addition to these phases, we find a superconducting phase that intrudes between them. For ω0/t =1 , superconductivity emerges when both U /t and 2 g2/t ω0 are small; then, by increasing the value of the phonon energy ω0, it extends along the transition line between antiferromagnetic and charge-density-wave insulators. Away from half filling, phase separation occurs when doping the charge-density-wave insulator, while a uniform (superconducting) ground state is found when doping the superconducting phase. In the analysis of finite-size effects, it is extremely important to average over twisted boundary conditions, especially in the weak-coupling limit and in the doped case.

  11. Two-Dimensional Massless Dirac Fermions in Antiferromagnetic AFe_{2}As_{2} (A=Ba,Sr).

    Science.gov (United States)

    Chen, Zhi-Guo; Wang, Luyang; Song, Yu; Lu, Xingye; Luo, Huiqian; Zhang, Chenglin; Dai, Pengcheng; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel

    2017-09-01

    We report infrared studies of AFe_{2}As_{2} (A=Ba, Sr), two representative parent compounds of iron-arsenide superconductors, at magnetic fields (B) up to 17.5 T. Optical transitions between Landau levels (LLs) were observed in the antiferromagnetic states of these two parent compounds. Our observation of a sqrt[B] dependence of the LL transition energies, the zero-energy intercepts at B=0  T under the linear extrapolations of the transition energies and the energy ratio (∼2.4) between the observed LL transitions, combined with the linear band dispersions in two-dimensional (2D) momentum space obtained by theoretical calculations, demonstrates the existence of massless Dirac fermions in the antiferromagnet BaFe_{2}As_{2}. More importantly, the observed dominance of the zeroth-LL-related absorption features and the calculated bands with extremely weak dispersions along the momentum direction k_{z} indicate that massless Dirac fermions in BaFe_{2}As_{2} are 2D. Furthermore, we find that the total substitution of the barium atoms in BaFe_{2}As_{2} by strontium atoms not only maintains 2D massless Dirac fermions in this system, but also enhances their Fermi velocity, which supports that the Dirac points in iron-arsenide parent compounds are topologically protected.

  12. Electrical switching of antiferromagnets via strongly spin-orbit coupled materials

    Science.gov (United States)

    Li, Xi-Lai; Duan, Xiaopeng; Semenov, Yuriy G.; Kim, Ki Wook

    2017-01-01

    Electrically controlled ultra-fast switching of an antiferromagnet (AFM) is shown to be realizable by interfacing it with a material of strong spin-orbit coupling. The proximity interaction between the sublattice magnetic moments of a layered AFM and the spin-polarized free electrons at the interface offers an efficient way to manipulate antiferromagnetic states. A quantitative analysis, using the combination with a topological insulator as an example, demonstrates highly reliable 90° and 180° rotations of AFM magnetic states under two different mechanisms of effective torque generation at the interface. The estimated switching speed and energy requirement are in the ps and aJ ranges, respectively, which are about two-three orders of magnitude better than the ferromagnetic counterparts. The observed differences in the magnetization dynamics may explain the disparate characteristic responses. Unlike the usual precessional/chiral motions in the ferromagnets, those of the AFMs can essentially be described as a damped oscillator with a more direct path. The impact of random thermal fluctuations is also examined.

  13. Electrically tunable transport in antiferromagnetic Sr3Ir2O7

    Science.gov (United States)

    Seinige, Heidi; Wang, Cheng; Cao, Gang; Zhou, Jianshi-S.; Goodenough, John B.; Tsoi, Maxim

    Recently we demonstrated experimentally the existence of interconnections between magnetic state and transport currents in antiferromagnetic (AFM) Mott insulator Sr2IrO4. We found a very large anisotropic magnetoresistance and demonstrated a reversible resistive switching driven by high-density currents/high electric fields. These results support the feasibility of AFM spintronics, where antiferromagnets are used in place of ferromagnets, however a low Néel temperature of this material (240 K) questions any practical applications. Here we present a comparative electrical transport study of its sister compound Sr2IrO4 which has a higher transition temperature (285 K). Similar to the case of Sr2IrO4, we find a continuous reduction in the resistivity of Sr3Ir2O7 as a function of increasing electrical bias and abrupt reversible changes above a threshold bias current. We explain these results by a reduction of activation energy associated with a field-driven lattice distortion. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, and by NSF Grants DMR-1207577, DMR-1265162, and DMR-1122603.

  14. Spin Seebeck effect in the antiferromagnet nickel oxide at room temperature

    Science.gov (United States)

    Holanda, J.; Maior, D. S.; Alves Santos, O.; Vilela-Leão, L. H.; Mendes, J. B. S.; Azevedo, A.; Rodríguez-Suárez, R. L.; Rezende, S. M.

    2017-10-01

    The generation of spin currents by thermal gradients applied to a magnetic film is known as the spin Seebeck effect (SSE). The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film produced by the spin to charge current conversion through the inverse spin Hall effect (ISHE). The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin orbit coupling, such as platinum. Recently, the SSE has been observed in bilayers made of the antiferromagnets MnF2 and Cr2O3 with Pt at low temperatures and high magnetic fields. Here, we report measurements of the SSE at room temperature and low magnetic fields in bilayers made of well textured films of antiferromagnetic NiO with several metals. The detection of the spin current generated by the thermal gradient in the NiO layer is made by means of the ISHE in the nonmagnetic metals Pt and Ta, in the AF metal IrMn, and in the ferromagnetic metal Ni81Fe19 (permalloy). The measured spin Seebeck effect in NiO/Pt has the same sign and is about one order of magnitude smaller than in YIG/Pt.

  15. Fractionalized excitations in the spin-liquid state of a kagome-lattice antiferromagnet.

    Science.gov (United States)

    Han, Tian-Heng; Helton, Joel S; Chu, Shaoyan; Nocera, Daniel G; Rodriguez-Rivera, Jose A; Broholm, Collin; Lee, Young S

    2012-12-20

    The experimental realization of quantum spin liquids is a long-sought goal in physics, as they represent new states of matter. Quantum spin liquids cannot be described by the broken symmetries associated with conventional ground states. In fact, the interacting magnetic moments in these systems do not order, but are highly entangled with one another over long ranges. Spin liquids have a prominent role in theories describing high-transition-temperature superconductors, and the topological properties of these states may have applications in quantum information. A key feature of spin liquids is that they support exotic spin excitations carrying fractional quantum numbers. However, detailed measurements of these 'fractionalized excitations' have been lacking. Here we report neutron scattering measurements on single-crystal samples of the spin-1/2 kagome-lattice antiferromagnet ZnCu(3)(OD)(6)Cl(2) (also called herbertsmithite), which provide striking evidence for this characteristic feature of spin liquids. At low temperatures, we find that the spin excitations form a continuum, in contrast to the conventional spin waves expected in ordered antiferromagnets. The observation of such a continuum is noteworthy because, so far, this signature of fractional spin excitations has been observed only in one-dimensional systems. The results also serve as a hallmark of the quantum spin-liquid state in herbertsmithite.

  16. Effect of thermal cycle on the interfacial antiferromagnetic spin configuration and exchange bias in Ni-Mn-Sb alloy

    Directory of Open Access Journals (Sweden)

    R. L. Wang

    2012-09-01

    Full Text Available Effect of thermal cycle on the interfacial antiferromagnetic (AFM spin configuration and exchange bias in Ni50Mn36Sb14 alloy has been investigated. The results indicate thermal cycle can induce further martensitic transition from part of arrested FM phase to AFM phase, leading to the reconstruction of interfacial antiferromagnetic spin configuration. The shape of hysteresis loops at 5 K after cooling back can be tuned from a single-shifted loop to a nearly symmetric double-shifted loop gradually accompanied with exchange bias field increasing to peak value and then decreasing. The evolutions can be illustrated intuitively by a simple AFM bidomain model.

  17. Resistive properties and phase diagram of the organic antiferromagnetic metal $\\kappa$-(BETS)$_2$FeCl$_4$

    OpenAIRE

    Kunz, Michael; Biberacher, Werner; Kushch, Natalia D.; Miyazaki, Akira; Kartsovnik, Mark. V.

    2016-01-01

    The low-temperature electronic state of the layered organic charge-transfer salt $\\kappa$-(BETS)$_2$FeCl$_4$ was probed by interlayer electrical resistance measurements under magnetic field. Both above and below $T_{\\mathrm{N}}=0.47\\,$K, the temperature of antiferromagnetic ordering of $3d$-electron spins of Fe$^{3+}$ localized in the insulating anion layers, a non-saturating linear $R(T)$ dependence has been observed. A weak superconducting signal has been detected in the antiferromagnetic s...

  18. Carrier Doping Effects on the Physical Properties of the Layered Antiferromagnetic Semiconductor (LaO)MnAs

    Science.gov (United States)

    Naito, Akito; Morosawa, Yasuhiro; Watanabe, Tadataka; Takano, Yoshiki; Takase, Kouichi

    We have focused on the layered antiferromagnetic semiconductor (LaO)MnAs and investigated carrier dependences of the physical properties to understand the semiconducting origin. The absolute values of electrical resistivity of (LaO1-xFx)MnAs decrease with F substitution, but the Zn substitution samples don't show apparent dependences in the resistivity. All substituted samples indicate paramagnetic behaviors, where (LaO)ZnAs without magnetic moments presents very small temperature independent magnetization. The magnetism of (LaO)MnAs changes from antiferromagnetism to paramagnetism by the carrier doping.

  19. The role of second nearest neighbor antiferromagnetic spin coupling in the orbitally ordered CMR manganites: A tight binding model study

    Science.gov (United States)

    Panda, Saswati; Santi, N.; Sahoo, D. D.; Rout, G. C.

    2017-05-01

    We report here a tight binding model study of the interplay of antiferromagnetic and orbital orderings in CMR manganites. The model consists of double exchange interaction, Heisenberg type antiferromagnetic spin interaction and band Jahn-Teller (JT) interaction along with kinetic energies of conduction band and core band electrons. Further, first and second nearest neighbor interactions are considered in the band energy dispersion and Heisenberg spin interaction. The model Hamiltonian is solved using Zubarev's Green's function technique and the interplay between transverse spin fluctuation and JT distortion is studied. The electron specific heat exhibits two peak structure near the transition temperatures as observed in experiments.

  20. Identification of ground-state spin ordering in antiferromagnetic transition metal oxides using the Ising model and a genetic algorithm.

    Science.gov (United States)

    Lee, Kyuhyun; Youn, Yong; Han, Seungwu

    2017-01-01

    We identify ground-state collinear spin ordering in various antiferromagnetic transition metal oxides by constructing the Ising model from first-principles results and applying a genetic algorithm to find its minimum energy state. The present method can correctly reproduce the ground state of well-known antiferromagnetic oxides such as NiO, Fe2O3, Cr2O3 and MnO2. Furthermore, we identify the ground-state spin ordering in more complicated materials such as Mn3O4 and CoCr2O4.

  1. Magnetic susceptibilities of minerals

    Science.gov (United States)

    Rosenblum, Sam; Brownfield, I.K.

    2000-01-01

    Magnetic separation of minerals is a topic that is seldom reported in the literature for two reasons. First, separation data generally are byproducts of other projects; and second, this study requires a large amount of patience and is unusually tedious. Indeed, we suspect that most minerals probably are never investigated for this property. These data are timesaving for mineralogists who concentrate mono-mineralic fractions for chemical analysis, age dating, and for other purposes. The data can certainly be used in the ore-beneficiation industries. In some instances, magnetic-susceptibility data may help in mineral identification, where other information is insufficient. In past studies of magnetic separation of minerals, (Gaudin and Spedden, 1943; Tille and Kirkpatrick, 1956; Rosenblum, 1958; Rubinstein and others, 1958; Flinter, 1959; Hess, 1959; Baker, 1962; Meric and Peyre, 1963; Rojas and others, 1965; and Duchesne, 1966), the emphasis has been on the ferromagnetic and paramagnetic ranges of extraction. For readers interested in the history of magnetic separation of minerals, Krumbein and Pettijohn (1938, p. 344-346) indicated nine references back to 1848. The primary purpose of this paper is to report the magnetic-susceptibility data on as many minerals as possible, similar to tables of hardness, specific gravity, refractive indices, and other basic physical properties of minerals. A secondary purpose is to demonstrate that the total and best extraction ranges are influenced by the chemistry of the minerals. The following notes are offered to help avoid problems in separating a desired mineral concentrate from mixtures of mineral grains.

  2. Graphene susceptibility in Holstein model

    Energy Technology Data Exchange (ETDEWEB)

    Mousavi, Hamze, E-mail: hamze.mousavi@gmail.co [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Nano Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of)

    2011-06-15

    We study the effects of the electron-phonon interaction on the temperature dependence of the orbital magnetic susceptibility of monolayer graphene. We use the linear response theory and Green's function formalism within the Holstein Hamiltonian model. The results show that the effects of the electron-phonon interaction on the susceptibility of graphene sheet have different behaviors in two temperature regions. In the low temperature region, susceptibility increases when the electron-phonon coupling strength increases. On the other hand, the susceptibility reduces with increasing the electron-phonon coupling strength in the high temperature region. - Highlights: Effect of electron-phonon interaction on the susceptibility of graphene is studied. Linear response theory and Green's function technique in Holstein model are used. Effect of electron-phonon on susceptibility has different behaviors in two temperature regions.

  3. Topological susceptibility from slabs

    Energy Technology Data Exchange (ETDEWEB)

    Bietenholz, Wolfgang [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P. 70-543, Distrito Federal, C.P. 04510 (Mexico); Forcrand, Philippe de [Institute for Theoretical Physics, ETH Zürich,CH-8093 Zürich (Switzerland); CERN, Physics Department, TH Unit, CH-1211 Geneva 23 (Switzerland); Gerber, Urs [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P. 70-543, Distrito Federal, C.P. 04510 (Mexico); Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo,Edificio C-3, Apdo. Postal 2-82, Morelia, Michoacán, C.P. 58040 (Mexico)

    2015-12-14

    In quantum field theories with topological sectors, a non-perturbative quantity of interest is the topological susceptibility χ{sub t}. In principle it seems straightforward to measure χ{sub t} by means of Monte Carlo simulations. However, for local update algorithms and fine lattice spacings, this tends to be difficult, since the Monte Carlo history rarely changes the topological sector. Here we test a method to measure χ{sub t} even if data from only one sector are available. It is based on the topological charges in sub-volumes, which we denote as slabs. Assuming a Gaussian distribution of these charges, this method enables the evaluation of χ{sub t}, as we demonstrate with numerical results for non-linear σ-models.

  4. Topological Susceptibility from Slabs

    CERN Document Server

    Bietenholz, Wolfgang; Gerber, Urs

    2015-01-01

    In quantum field theories with topological sectors, a non-perturbative quantity of interest is the topological susceptibility chi_t. In principle it seems straightforward to measure chi_t by means of Monte Carlo simulations. However, for local update algorithms and fine lattice spacings, this tends to be difficult, since the Monte Carlo history rarely changes the topological sector. Here we test a method to measure chi_t even if data from only one sector are available. It is based on the topological charges in sub-volumes, which we denote as slabs. Assuming a Gaussian distribution of these charges, this method enables the evaluation of chi_t, as we demonstrate with numerical results for non-linear sigma-models.

  5. Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs{sub 2}CuCl{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Cong, P. T., E-mail: t.pham@hzdr.de [Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Postulka, L.; Wolf, B.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M., E-mail: michael.lang@physik.uni-frankfurt.de [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Well, N. van [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (Switzerland)

    2016-10-14

    Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs{sub 2}CuCl{sub 4} were performed for the longitudinal modes c{sub 11} and c{sub 33} in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at T{sub N}. Isothermal measurements at T < T{sub N} of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at B{sub s} ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature T{sub N}(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/k{sub B} ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.

  6. Antiferromagnetism, crystal fields and hybridisation in UxY1-xPd3 studied by neutron scattering

    DEFF Research Database (Denmark)

    Bull, M.J.; McEwen, K.A.; Eccleston, R.S.

    1999-01-01

    We summarise our UxY1-xPd3 inelastic neutron scattering experiments and present new neutron diffraction results for a single crystal of U0.45Y0.55Pd3. Long-range antiferromagnetic order is unambiguously observed below T-N = 22.5 K. in contrast, no long-range order is found in polycrystalline...

  7. Co-existence of ferromagnetic and antiferromagnetic interactions in Mn3Ga(1-x)Sn x C

    Science.gov (United States)

    Dias, E. T.; Priolkar, K. R.; Nigam, A. K.

    2014-04-01

    The magnetic properties of the \\text{M}{{\\text{n}}_{3}}\\text{G}{{\\text{a}}_{(1-x)}}\\text{S}{{\\text{n}}_{x}}\\text{C}, 0\\leqslant x\\leqslant 1 antiperovskite compounds have been investigated in detail. Though all compounds of this series crystallize in a cubic structure, the Ga rich (x\\leqslant 0.2) compounds transform, via a first-order transformation, to an antiferromagnetic ground state and the Sn rich (x\\geqslant 0.8) compounds exhibit dominant ferromagnetic interactions at low temperature. In the intermediate range (0.4\\leqslant x\\leqslant 0.7) co-existence of ferromagnetic and antiferromagnetic interactions can be seen. The results have been explained to be due to growth of ferromagnetic sub-lattice at the expense of antiferromagnetic sub-lattice with increasing Sn concentration in \\text{M}{{\\text{n}}_{3}}\\text{G}{{\\text{a}}_{(1-x)}}\\text{S}{{\\text{n}}_{x}}\\text{C}. This growth occurs to a point where the first-order transition is altered from a ferromagnetic-antiferromagnetic type in Ga rich compounds to a paramagnetic-ferrimagnetic type in \\text{M}{{\\text{n}}_{3}}\\text{SnC}.

  8. Ferrimagnetic-antiferromagnetic phase transition in Mn2–xCrxSb : Electronic structure and electrical and magnetic properties

    NARCIS (Netherlands)

    Wijngaard, Jan; Haas, C.; Groot, R.A. de

    1992-01-01

    Self-consistent spin-polarized energy-band calculations have been performed for Mn2Sb for a ferrimagnetic (FI), ferromagnetic (F), and antiferromagnetic (AF) spin alignment. The calculated local moments on the two types of Mn atoms are in agreement with values obtained from neutron diffraction for

  9. Electrically tunable transport and high-frequency dynamics in antiferromagnetic S r3I r2O7

    Science.gov (United States)

    Seinige, Heidi; Williamson, Morgan; Shen, Shida; Wang, Cheng; Cao, Gang; Zhou, Jianshi; Goodenough, John B.; Tsoi, Maxim

    2016-12-01

    We report dc and high-frequency transport properties of antiferromagnetic S r3I r2O7 . Temperature-dependent resistivity measurements show that the activation energy of this material can be tuned by an applied dc electrical bias. The latter allows for continuous variations in the sample resistivity of as much as 50% followed by a reversible resistive switching at higher biases. Such a switching is of high interest for antiferromagnetic applications in high-speed memory devices. Interestingly, we found the switching behavior to be strongly affected by a high-frequency (microwave) current applied to the sample. The microwaves at 3-7 GHz suppress the dc switching and produce resonancelike features that we tentatively associated with the dissipationless magnonics recently predicted to occur in antiferromagnetic insulators subject to ac electric fields. We have characterized the effects of microwave irradiation on electronic transport in S r3I r2O7 as a function of microwave frequency and power, strength and direction of external magnetic field, strength and polarity of applied dc bias, and temperature. Our observations support the potential of antiferromagnetic materials for high-speed/high-frequency spintronic applications.

  10. Correlation between peak and median blocking temperatures by magnetization measurement on isolated ferromagnetic and antiferromagnetic particle systems

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Mørup, Steen

    1997-01-01

    The influence of the particle size distribution on the ratio of the peak temperature, T-peak, to the blocking temperature, T-Bm, in zero field cooled (ZFD) magnetization curves has studied for both ferromagnetic and antiferromagnetic particle systems. In both systems the ratio beta=T-peak/T-Bm does...

  11. Nonlinear Effects in the Dynamic Structure Factor of the Classical Antiferromagnetic Heisenberg Chain in an External Field at Low Temperatures

    NARCIS (Netherlands)

    Raedt, B. De; Raedt, H. De; Fivez, J.

    1981-01-01

    Is is found that nonlinear effects give rise to anomalies in the spectrum of the antiferromagnetic Heisenberg chain in an external field, even at low temperatures. Divergences in the two-magnon density of states are responsible for additional resonances, besides the usual spin-wave peak, in the

  12. Evolution of magnetic states in frustrated diamond lattice antiferromagnetic Co(Al1-xCox)(2)O-4 spinels

    DEFF Research Database (Denmark)

    Zaharko, O.; Cervellino, A.; Tsurkan, V.

    2010-01-01

    Using neutron powder diffraction and Monte Carlo simulations we show that a spin-liquid regime emerges at all compositions in the diamond-lattice antiferromagnets Co(Al1−xCox)2O4. This spin-liquid regime induced by frustration due to the second-neighbor exchange coupling J2 is gradually superseded...

  13. Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4

    DEFF Research Database (Denmark)

    Zaharko, O.; Christensen, Niels Bech; Cervellino, A.

    2011-01-01

    We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg pea...

  14. Nutrition affects insect susceptibility to Bt toxins

    Science.gov (United States)

    Deans, Carrie A.; Behmer, Spencer T.; Tessnow, Ashley E.; Tamez-Guerra, Patricia; Pusztai-Carey, Marianne; Sword, Gregory A.

    2017-01-01

    Pesticide resistance represents a major challenge to global food production. The spread of resistance alleles is the primary explanation for observations of reduced pesticide efficacy over time, but the potential for gene-by-environment interactions (plasticity) to mediate susceptibility has largely been overlooked. Here we show that nutrition is an environmental factor that affects susceptibility to Bt toxins. Protein and carbohydrates are two key macronutrients for insect herbivores, and the polyphagous pest Helicoverpa zea self-selects and performs best on diets that are protein-biased relative to carbohydrates. Despite this, most Bt bioassays employ carbohydrate-biased rearing diets. This study explored the effect of diet protein-carbohydrate content on H. zea susceptibility to Cry1Ac, a common Bt endotoxin. We detected a 100-fold increase in LC50 for larvae on optimal versus carbohydrate-biased diets, and significant diet-mediated variation in survival and performance when challenged with Cry1Ac. Our results suggest that Bt resistance bioassays that use ecologically- and physiologically-mismatched diets over-estimate susceptibility and under-estimate resistance.

  15. Antibiotic Susceptibility of Potentially Probiotic Vaginal Lactobacilli

    Directory of Open Access Journals (Sweden)

    Virginia Ocaña

    2006-01-01

    Full Text Available Objective. To study the antimicrobial susceptibility of six vaginal probiotic lactobacilli. Methods. The disc diffusion method in Müeller Hinton, LAPTg and MRS agars by the NCCLS (National Committee for Clinical Laboratory Standards procedure was performed. Due to the absence of a Lactobacillus reference strains, the results were compared to those of Staphylococcus aureus ATCC29213. Minimal Inhibitory Concentration (MIC with 21 different antibiotics in LAPTg agar and broth was also determined. Results. LAPTg and MRS agars are suitable media to study antimicrobial susceptibility of lactobacilli. However, the NCCLS procedure needs to be standardized for this genus. The MICs have shown that all Lactobacillus strains grew at concentrations above 10 μg/mL of chloramphenicol, aztreonam, norfloxacin, ciprofloxacin, ceftazidime, ceftriaxone, streptomycin and kanamycin. Four lactobacilli were sensitive to 1 μg/mL vancomycin and all of them were resistant to 1000 μg/mL of metronidazole. Sensitivity to other antibiotics depended on each particular strain. Conclusions. The NCCLS method needs to be standardized in an appropriate medium to determine the antimicrobial susceptibility of Lactobacillus. Vaginal probiotic lactobacilli do not display uniform susceptibility to antibiotics. Resistance to high concentrations of metronidazole suggests that lactobacilli could be simultaneously used with a bacterial vaginosis treatment to restore the vaginal normal flora.

  16. Antibiotic Susceptibility of Potentially Probiotic Vaginal Lactobacilli

    Science.gov (United States)

    Ocaña, Virginia; Silva, Clara; Nader-Macías, María Elena

    2006-01-01

    Objective. To study the antimicrobial susceptibility of six vaginal probiotic lactobacilli. Methods. The disc diffusion method in Müeller Hinton, LAPTg and MRS agars by the NCCLS (National Committee for Clinical Laboratory Standards) procedure was performed. Due to the absence of a Lactobacillus reference strains, the results were compared to those of Staphylococcus aureus ATCC29213. Minimal Inhibitory Concentration (MIC) with 21 different antibiotics in LAPTg agar and broth was also determined. Results. LAPTg and MRS agars are suitable media to study antimicrobial susceptibility of lactobacilli. However, the NCCLS procedure needs to be standardized for this genus. The MICs have shown that all Lactobacillus strains grew at concentrations above 10 μg/mL of chloramphenicol, aztreonam, norfloxacin, ciprofloxacin, ceftazidime, ceftriaxone, streptomycin and kanamycin. Four lactobacilli were sensitive to 1 μg/mL vancomycin and all of them were resistant to 1000 μg/mL of metronidazole. Sensitivity to other antibiotics depended on each particular strain. Conclusions. The NCCLS method needs to be standardized in an appropriate medium to determine the antimicrobial susceptibility of Lactobacillus. Vaginal probiotic lactobacilli do not display uniform susceptibility to antibiotics. Resistance to high concentrations of metronidazole suggests that lactobacilli could be simultaneously used with a bacterial vaginosis treatment to restore the vaginal normal flora. PMID:17485797

  17. Control of antiferromagnetic spin axis orientation in bilayer Fe/CuMnAs films.

    Science.gov (United States)

    Wadley, P; Edmonds, K W; Shahedkhah, M R; Campion, R P; Gallagher, B L; Železný, J; Kuneš, J; Novák, V; Jungwirth, T; Saidl, V; Němec, P; Maccherozzi, F; Dhesi, S S

    2017-09-11

    Using x-ray magnetic circular and linear dichroism techniques, we demonstrate a collinear exchange coupling between an epitaxial antiferromagnet, tetragonal CuMnAs, and an Fe surface layer. A small uncompensated Mn magnetic moment is observed which is antiparallel to the Fe magnetization. The staggered magnetization of the 5 nm thick CuMnAs layer is rotatable under small magnetic fields, due to the interlayer exchange coupling. This allows us to obtain the x-ray magnetic linear dichroism spectra for different crystalline orientations of CuMnAs in the (001) plane. This is a key parameter for enabling the understanding of domain structures in CuMnAs imaged using x-ray magnetic linear dichroism microscopy techniques.

  18. Solitary Magnons in the S =5/2 Antiferromagnet CaFe2O4

    Science.gov (United States)

    Stock, C.; Rodriguez, E. E.; Lee, N.; Green, M. A.; Demmel, F.; Ewings, R. A.; Fouquet, P.; Laver, M.; Niedermayer, Ch.; Su, Y.; Nemkovski, K.; Rodriguez-Rivera, J. A.; Cheong, S.-W.

    2016-07-01

    CaFe2O4 is a S =5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c -axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ˜1 ns at the onset of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions ˜1 - 2 c -axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A +B orders as well as localization of spin excitations in a classical magnet.

  19. Theoretical reconsideration of antiferromagnetic Fermi surfaces in URu{sub 2}Si{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Yamagami, Hiroshi, E-mail: yamagami@cc.kyoto-su.ac.jp [Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555 (Japan)

    2011-01-01

    In an itinerant 5f-band model, the antiferromagnetic (AFM) Fermi surfaces of URu{sub 2}Si{sub 2} are reconsidered using a relativistic LAPW method within a local spin-density approximation, especially taking into account the lattice parameters dependent on pressures. The reduction of the z-coordinate of the Si sites results in the effect of flattening the Ru-Si layers of URu{sub 2}Si{sub 2} crystal structure, thus weakening a hybridization/mixing between the U-5f and Ru-4d states in the band structure. Consequently the 5f bands around the Fermi level are more flat in the dispersion with decreasing the z-coordinate, thus producing three closed Fermi surfaces like 'curing-stone', 'rugby-ball' and 'ball'. The origins of de Haas-van Alphen branches can be qualitatively interpreted from the obtained AFM Fermi surfaces.

  20. Proposal of a general scheme to obtain room-temperature spin polarization in asymmetric antiferromagnetic semiconductors

    Science.gov (United States)

    Li, Xingxing; Wu, Xiaojun; Li, Zhenyu; Yang, Jinlong

    2015-09-01

    Exploring magnetic semiconductors is one of the most important questions for spintronic applications. Although various solutions, such as dilute magnetic semiconductors, have been proposed, a practical spintronic device working at room temperature has not been realized. The key to address this issue is to find magnetic materials with both room-temperature magnetic ordering and large spin polarization around the Fermi energy level. Here, we predict a new concept of asymmetric antiferromagnetic (AFM) semiconductors (AAFMSs) with both features. The high temperature magnetic ordering originates from the AFM coupling between different transition metal ions with strong super-exchange interaction, whereas the large spin polarization around the Fermi energy level owes to d orbital mismatch among these ions. Through first-principles calculations, a family of double perovskites A2Cr M O6 (A =Ca ,Sr ,Ba , and M =Ru ,Os ) are predicted to be AAFMSs. This paper provides a way for developing spintronic devices working at room temperature.

  1. Spin waves in the fcc lattice antiferromagnet: competing interactions, frustration, and instabilities in the Hubbard model

    Science.gov (United States)

    Singh, Avinash; Mohapatra, Shubhajyoti; Ziman, Timothy; Chatterji, Tapan

    2017-02-01

    Spin waves in the type-III ordered antiferromagnetic state of the frustrated t- t ' Hubbard model on the face-centred-cubic (fcc) lattice are calculated to investigate finite-U-induced competing interaction and frustration effects on magnetic excitations and instabilities. Particularly strong competing interactions generated due to the interplay of fcc lattice geometry and magnetic order result in significant spin wave softening. The calculated spin wave dispersion is found to be in qualitative agreement with the measured spin wave dispersion in the pyrite mineral MnS2 obtained from inelastic neutron scattering experiments. Instabilities to other magnetic orders (type I, type II, spiral, non-collinear), as signalled by spin wave energies turning negative, are also discussed.

  2. Chiral Spin Liquid on a Kagome Antiferromagnet Induced by the Dzyaloshinskii-Moriya Interaction

    Science.gov (United States)

    Messio, Laura; Bieri, Samuel; Lhuillier, Claire; Bernu, Bernard

    2017-06-01

    The quantum spin liquid material herbertsmithite is described by an antiferromagnetic Heisenberg model on the kagome lattice with a non-negligible Dzyaloshinskii-Moriya interaction (DMI). A well-established phase transition to the q =0 long-range order occurs in this model when the DMI strength increases, but the precise nature of a small-DMI phase remains controversial. Here, we describe a new phase obtained from Schwinger-boson mean-field theory that is stable at small DMI, and which can explain the dispersionless spectrum seen in the inelastic neutron scattering experiment by Han et al. [Nature (London) 492, 406 (2012), 10.1038/nature11659]. It is a time-reversal symmetry breaking Z2 spin liquid, with the unique property of a small and constant spin gap in an extended region of the Brillouin zone. The phase diagram as a function of DMI and spin size is given, and dynamical spin structure factors are presented.

  3. Antiferromagnetic coupling of TbPc2 molecules to ultrathin Ni and Co films

    Directory of Open Access Journals (Sweden)

    David Klar

    2013-05-01

    Full Text Available The magnetic and electronic properties of single-molecule magnets are studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We study the magnetic coupling of ultrathin Co and Ni films that are epitaxially grown onto a Cu(100 substrate, to an in situ deposited submonolayer of TbPc2 molecules. Because of the element specificity of the X-ray absorption spectroscopy we are able to individually determine the field dependence of the magnetization of the Tb ions and the Ni or Co film. On both substrates the TbPc2 molecules couple antiferromagnetically to the ferromagnetic films, which is possibly due to a superexchange interaction via the phthalocyanine ligand that contacts the magnetic surface.

  4. Structural and magnetic properties of antiferromagnetic Heusler Ru2MnGe Epitaxial thin films

    Science.gov (United States)

    Fukatani, Naoto; Fujita, Hirohito; Miyawaki, Tetsuya; Ueda, Kenji; Asano, Hidefumi

    2013-08-01

    Structural and magnetic properties were investigated for Heusler-type alloy Ru2MnGe thin films. Ru2MnGe films on MgO substrate were subjected to an in-plane compressive strain, and exhibited enhanced antiferromagnetic (AFM) transition temperature ( T N ) up to 353 K, which exceeds by 37 K from the cubic bulk material ( T N = 316 K). We also observed the exchange coupling between Ru2MnGe and Heusler-type ferromagnetic (FM) half-metal Fe2CrSi thin films. The present AFM Heusler alloy with relatively high T N is useful to fabricate high-quality all Heusler-type half-metal AFM/FM junctions and is a promising material for the emerging field of AFM spintronics.

  5. Pressure-induced metallic ferromagnetism in antiferromagnetic insulator LaMnAsO

    Science.gov (United States)

    Tang, HuaiBao; Li, Guang; Yang, Qun; Zuo, XueQing; Zhang, HaiJun; Liu, DaYong

    2017-05-01

    Based on the first-principles calculations, we investigate the effects of the hydrostatic pressure on the layered oxypnictide LaMnAsO, and predict that it undergoes a transition from a G-type antiferromagnetic (AFM) insulator to a ferromagnetic (FM) metal at the critical pressure Pc ∼ 18.0 GPa, accompanied by a high-spin state with (mMn = 2.65 μB) to low-spin mMn = 1.63 μB transition, or magnetic moment collapse. Our calculations identify that it is the hydrostatic pressure that collapses the G-type AFM gap, and the large density of state (DOS) around Fermi level stabilizes the FM metallic phase due to the Stoner instability. The pressure-induced AFM insulator to FM metal transition opens up the possibility of two state device applications in the oxypnictide LaMnAsO compound.

  6. Dynamics of a driven spin coupled to an antiferromagnetic spin bath

    Energy Technology Data Exchange (ETDEWEB)

    Yuan Xiaozhong; Goan, Hsi-Sheng [Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan (China); Zhu, Ka-Di, E-mail: goan@phys.ntu.edu.tw [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2011-02-15

    We study the behavior of the Rabi oscillations of a driven central spin (qubit) coupled to an antiferromagnetic spin bath (environment). It is found that the decoherence behavior of the central spin depends on the detuning, driving strength, qubit-bath coupling and an important factor {Omega}, associated with the number of coupled atoms, the detailed lattice structure and the temperature of the environment. If detuning exists, Rabi oscillations may show the behavior of collapses and revivals; however, if detuning is absent, such a behavior will not appear. We investigate the weighted frequency distribution of the time evolution of the central spin inversion and give a reasonable explanation of this phenomenon of collapses and revivals. We also discuss the decoherence and pointer states of the qubit from the perspective of von Neumann entropy. We found that the eigenstates of the qubit self-Hamiltonian emerge as pointer states in the weak system-environment coupling limit.

  7. Magnetic interactions in geometrically frustrated triangular lattice antiferromagnet CuFeO2

    Science.gov (United States)

    Fernandez-Baca, Jaime; Ye, Feng; Fishman, Randy; Kang, H. J.; Lynn, J. W.; Kimura, Tsuyoshi

    2008-03-01

    Geometrically frustrated magnetic systems have received considerable attention due to their extraordinary magnetic properties. The delafossite CuFeO2 is of particular interest because it exhibits multiferroic behavior with either the application of a magnetic field or introduction of nonmagnetic impurities. Our recent [1] on CuFeO2 shows that spin waves in this material can be explained by antiferromagnetic interactions up to third nearest neighbors within the hexagonal plane as well as out-of-plane coupling, indicating that the quasi-like Ising nature of this material results from the delicate balance between competing interactions. Two energy dips in the spin wave dispersion occur at the incommensurate wavevectors associated with multiferroic phase, and are dynamic precursors to the magnetoelectric behavior. In this talk we will present preliminary measurements of the field magnetic field dependence of these excitations as CuFeO2 approaches the multiferroic phase [1] Ye et al. Phys. Rev. Lett. 99, 157201 (2007)

  8. Quantum phase transition between antiferromagnetic and charge order in the Hubbard-Holstein model

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, Johannes [Max-Planck Institute for Solid State Research, Heisenbergstr.1, 70569 Stuttgart (Germany); Hewson, Alex C. [Department of Mathematics, Imperial College, London SW7 2AZ (United Kingdom)

    2010-03-15

    We explore the quantum phase transitions between two ordered states in the infinite dimensional Hubbard-Holstein model at half filling. Our study is based on the dynamical mean field theory (DMFT) combined with the numerical renormalization group (NRG), which allows us to handle both strong electron-electron and strong electron-phonon interactions. The transition line is characterized by an effective electron-electron interaction. Depending on this effective interaction and the phonon frequency {omega}{sub 0} one finds either a continuous transition or discontinuous transition. Here, the analysis focuses on the behavior of the system when the electron-electron repulsion U and the phonon-mediated attraction {lambda} are equal. We first discuss the adiabatic and antiadiabatic limiting cases. For finite {omega}{sub 0} we study the differences between the antiferromagnetic (AFM) and charge order, and find that when present the AFM state has a lower energy on the line. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  9. Monte Carlo study of the Ising antiferromagnetic with a longitudinal field on the anisotropic square lattice

    Science.gov (United States)

    Viana, J. Roberto; Neto, Minos A.; de Sousa, J. Ricardo

    2009-06-01

    The Ising antiferromagnetic in the presence of a magnetic field on an anisotropic square lattice is studied by Monte Carlo simulation. We obtained the phase diagram in the T-H plane investigating the reentrant behavior around of the critical field H=2J. Using the Binder cumulant we locate the critical temperature T as a function of H. In order to test our simulation, for null field we obtain the critical behavior of T as a function of r=J/J and is in excellent agreement with exact solution of Onsager. Our results indicate a second-order transition for all values of H and particular case r=1 (independent of the ratio r≠0), where not reentrant behavior was observed.

  10. Monte Carlo study of the Ising antiferromagnetic with a longitudinal field on the anisotropic square lattice

    Energy Technology Data Exchange (ETDEWEB)

    Viana, J. Roberto; Neto, Minos A. [Departamento de Fisica, Universidade Federal do Amazonas, 3000 Japiim, 69077-000 Manaus-AM (Brazil); Sousa, J. Ricardo de, E-mail: jsousa@pq.cnpq.b [Departamento de Fisica, Universidade Federal do Amazonas, 3000 Japiim, 69077-000 Manaus-AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, 3000 Japiim, 69077-000 Manaus-AM (Brazil)

    2009-06-29

    The Ising antiferromagnetic in the presence of a magnetic field on an anisotropic square lattice is studied by Monte Carlo simulation. We obtained the phase diagram in the T-H plane investigating the reentrant behavior around of the critical field H{sub c}=2J{sub y}. Using the Binder cumulant we locate the critical temperature T{sub c} as a function of H. In order to test our simulation, for null field we obtain the critical behavior of T{sub c} as a function of r=J{sub y}/J{sub x} and is in excellent agreement with exact solution of Onsager. Our results indicate a second-order transition for all values of H and particular case r=1 (independent of the ratio rnot =0), where not reentrant behavior was observed.

  11. Comparison of dispersion and actuation properties of vortex and synthetic antiferromagnetic particles for biotechnological applications

    Science.gov (United States)

    Leulmi, S.; Joisten, H.; Dietsch, T.; Iss, C.; Morcrette, M.; Auffret, S.; Sabon, P.; Dieny, B.

    2013-09-01

    Magnetic nanoparticles are receiving an increasing interest for various biotechnological applications due to the capability that they offer to exert actuation on biological species via external magnetic fields. In this study, two types of magnetic particles recently proposed for cancer cells treatment were compared. Both are prepared by top-down approaches and imitate the properties of superparamagnetic particles. One type is made of a single magnetic layer and has a magnetic vortex configuration. The second type has a multilayered structure called synthetic antiferromagnet. Once released in solution, the agglomeration/dispersion of these particles due to their magnetostatic interactions was compared as well as the mechanical torque that they can generate when submitted to an external magnetic field.

  12. Theory of Topological Spin Hall Effect in Antiferromagnetic Skyrmion: Impact on Current-induced Motion

    KAUST Repository

    Akosa, Collins Ashu

    2017-09-09

    We demonstrate that the nontrivial magnetic texture of antiferromagnetic skyrmions (AFM-Sks) promotes a non-vanishing topological spin Hall effect (TSHE) on the flowing electrons. This results in a substantial enhancement of the non-adiabatic torque and hence improves the skyrmion mobility. This non-adiabatic torque increases when decreasing the skyrmion size, and therefore scaling down results in a much higher torque efficiency. In clean AFM-Sks, we find a significant boost of the TSHE close to van Hove singularity. Interestingly, this effect is enhanced away from the band gap in the presence of non-magnetic interstitial defects. Furthermore, unlike their ferromagnetic counterpart, TSHE in AFM-Sks increases with increase in disorder strength thus opening promising avenues for materials engineering of this effect.

  13. Gate-controllable magneto-optic Kerr effect in layered collinear antiferromagnets

    Science.gov (United States)

    Sivadas, Nikhil; Okamoto, Satoshi; Xiao, Di

    Using symmetry arguments and a tight-binding model, we show that for layered collinear antiferromagnets, magneto-optic effects can be generated and manipulated by controlling crystal symmetries through a gate voltage. This provides a promising route for electric field manipulation of the magneto-optic effects without modifying the underlying magnetic structure. We further demonstrate the gate control of magneto-optic Kerr effect (MOKE) in bilayer MnPSe3 using first-principles calculations. The field-induced inversion symmetry breaking effect leads to gate-controllable MOKE whose direction of rotation can be switched by the reversal of the gate voltage. This work is supported by AFOSR No. FA9550-12-1-0479 and FA9550-14-1-0277 and NSP No. EFRI-1433496.

  14. [mu][sup +]SR study of two-dimensional antiferromagnets, delafossite-type compounds

    Energy Technology Data Exchange (ETDEWEB)

    Mekata, M. (Dept. of Applied Physics, Fukui Univ. (Japan)); Yaguchi, N. (Dept. of Applied Physics, Fukui Univ. (Japan)); Kuriyama, H. (Dept. of Applied Physics, Fukui Univ. (Japan)); Asano, T. (Dept. of Applied Physics, Fukui Univ. (Japan)); Nagamine, K. (MSL, Dept. of Physics, Univ. of Tokyo (Japan)); Keren, A. (Physics Dept., Columbia Univ., New York, NY (United States)); Le, L.P. (Physics Dept., Columbia Univ., New York, NY (United States)); Luke, G.M. (Physics Dept., Columbia Univ., New York, NY (United States)); Wu, W.D. (Physics Dept., Columbia Univ., New York, NY (United States)); Uemura, Y.J. (Physics Dept., Columbia Univ., New York, NY (United States))

    1993-11-01

    [mu][sup +]SR experiments were performed on delafossite-type compounds, CuCrO[sub 2], AgCrO[sub 2], CuFeO[sub 2], which are model compounds of triangular lattice antiferromagnets. The initial asymmetries are much smaller than the expected value, implying muonium formation. The time spectra are composed of slow and fast relaxation components. We attributed the components to signals from [mu][sup +] stopped at the center of O[sup 2-] ions and muonium far from nuclear dipole moments, respectively. The asymmetries decrease below T[sub N] but no precession spectra were observed. Relaxation rates of slow and fast relaxation components show maxima at T[sub N]. (orig.)

  15. Graphic User Interface for Monte Carlo Simulation of Ferromagnetic/Antiferromagnetic Manganite Bilayers

    Directory of Open Access Journals (Sweden)

    Hector Barco-Ríos

    2011-06-01

    Full Text Available The manganites have been widely studied because of their important properties as colossal magnetoresistance and exchange bias that are important phenomena used in many technological applications. For this reason, in this work, a study of the exchange bias effect present in La2/3Ca1/3MnO3/La1/3Ca2/3MnO3. This study was carried out by using the Monte Carlo method and the Metropolis Algorithm. In order to make easy this study, a graphic user interface was built alloying a friendly interaction. The interface permits to control the thickness of Ferromagnetic and Antiferromagnetic layer, temperatures the magnetic field, the number of Monte Carlo steps and the exchange parameters. Results obtained reflected the influence of all of these parameters on the exchange bias and coercive fields.

  16. Electronic properties of antiferromagnetic UBi2 metal by exact exchange for correlated electrons method

    Directory of Open Access Journals (Sweden)

    E Ghasemikhah

    2012-03-01

    Full Text Available This study investigated the electronic properties of antiferromagnetic UBi2 metal by using ab initio calculations based on the density functional theory (DFT, employing the augmented plane waves plus local orbital method. We used the exact exchange for correlated electrons (EECE method to calculate the exchange-correlation energy under a variety of hybrid functionals. Electric field gradients (EFGs at the uranium site in UBi2 compound were calculated and compared with the experiment. The EFGs were predicted experimentally at the U site to be very small in this compound. The EFG calculated by the EECE functional are in agreement with the experiment. The densities of states (DOSs show that 5f U orbital is hybrided with the other orbitals. The plotted Fermi surfaces show that there are two kinds of charges on Fermi surface of this compound.

  17. Antiferromagnetic spin and twin domain walls govern hysteretic expressions of exchange anisotropy

    Science.gov (United States)

    Armstrong, Jason N.; Sullivan, Matthew R.; Chopra, Harsh Deep

    2009-09-01

    The present study shows that antiferromagnetic spin and twin domain walls govern the hysteretic expressions of exchange anisotropy at low and high fields, respectively, using annealed NiO single crystals and Co. In the presence of twin walls, spin walls are shown to be a geometrical necessity in the antiferromagnetic NiO. A threshold field (˜10000Oe) exists below which twin walls are frozen, and rotational hysteresis is dominated by losses due to spin walls. Above the threshold field, twin walls become mobile, resulting in a sharp increase in rotational hysteresis. Remarkably, rotational hysteresis associated with spin walls is similar to that of an ordinary ferromagnet—as the field strength increases, rotational hysteresis tends toward zero. However, unlike an ordinary ferromagnet where rotational hysteresis becomes zero above its saturation field, rotational hysteresis in antiferromagnet drops but then sharply increases once the threshold field for twin wall motion is exceeded. In crystals without spin walls, low-field rotational hysteresis is zero or negligible. Domain imaging of twin walls in antiferromagnet and Weiss walls in ferromagnet reveals a one-to-one spatial correlation even though twin walls are considered to have no net dipoles. This surprising result is explained by the fact that crystallographic interfaces in real crystals are not atomically sharp or ideal, and the defective interface invariably results in net moment across the finite width of the twin wall. The field dependence of domain walls in Co film exchange coupled to NiO shows global similarities to previously reported behavior of Co films deposited on nanocrystalline NiO [H. D. Chopra, D. X. Yang, P. J. Chen, H. J. Brown, L. J. Swartzendruber, and W. F. Egelhoff, Jr., Phys. Rev. B 61, 15312 (2000)]. In both cases, domain wall motion is not the dominant mode of magnetization reversal (wall motion is entirely absent in the present study while wall motion was only occasionally observed in

  18. Controlling frustrated liquids and solids with an applied field in a kagome Heisenberg antiferromagnet.

    Science.gov (United States)

    Nishimoto, Satoshi; Shibata, Naokazu; Hotta, Chisa

    2013-01-01

    Quantum spin-1/2 kagome Heisenberg antiferromagnet is the representative frustrated system possibly hosting a spin liquid. Clarifying the nature of this elusive topological phase is a key challenge in condensed matter; however, even identifying it still remains unsettled. Here we apply a magnetic field and discover a series of spin-gapped phases appearing at five different fractions of magnetization by means of a grand canonical density matrix renormalization group, an unbiased state-of-the-art numerical technique. The magnetic field dopes magnons and first gives rise to a possible Z₃ spin liquid plateau at 1/9 magnetization. Higher field induces a self-organized super-lattice unit, a six-membered ring of quantum spins, resembling an atomic orbital structure. Putting magnons into this unit one by one yields three quantum solid plateaus. We thus find that the magnetic field could control the transition between various emergent phases by continuously releasing the frustration.

  19. Design of half-metallic antiferromagnets: transition metal chalcogenides and pnictides

    Science.gov (United States)

    Akai, Hisazumi; Ogura, Masako; Hoang Long, Nguyen

    2010-03-01

    Half-metallic antiferromagnts are the materials that exhibit half-metallicity and antifirromagnetism (compensated ferrimagnetism) simultaneously. Such materials are especially useful for spintronics devices since they have 100 % spin-polarized Fermi surfaces despite of their robustness against a disturbance of external magnetic field. We found that (XY)Z2, where X and Y are transition metal elements and Z is a chalcogens or a pnictigen, show half-metallic antiferromagnetism when the sum of effective d electron numbers of X and Y is 10. Examples are (CrFe)S2 and (CrFe)Se2. We report a systematic investigation of the electronic structure and transport properties of these materials calculated by the KKR-Green's function method combined with the Kubo-Greenwood formula.

  20. Spin Pumping and Shot Noise in Ferrimagnets: Bridging Ferro- and Antiferromagnets

    Science.gov (United States)

    Kamra, Akashdeep; Belzig, Wolfgang

    2017-11-01

    A combination of novel technological and fundamental physics prospects has sparked a huge interest in pure spin transport in magnets, starting with ferromagnets and spreading to antiferro- and ferrimagnets. We present a theoretical study of spin transport across a ferrimagnet-nonmagnetic conductor interface, when a magnetic eigenmode is driven into a coherent state. The obtained spin current expression includes intra- as well as cross-sublattice terms, both of which are essential for a quantitative understanding of spin pumping. The dc current is found to be sensitive to the asymmetry in interfacial coupling between the two sublattice magnetizations and the mobile electrons, especially for antiferromagnets. We further find that the concomitant shot noise provides a useful tool for probing the quasiparticle spin and interfacial coupling.

  1. Coexistence of antiferromagnetism and superconductivity in CePt2In7

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, Eric D [Los Alamos National Laboratory; Sidorov, Vladimir A [Los Alamos National Laboratory; Lee, Han O [Los Alamos National Laboratory; Kurita, Nobuyuki [Los Alamos National Laboratory; Ronning, F [Los Alamos National Laboratory; Movshovich, R [Los Alamos National Laboratory; Thompson, J D [Los Alamos National Laboratory

    2009-01-01

    The physical properties of CePt{sub 2}In{sub 7} are presented at pressures up to 3.12 GPa. Antiferromagnetic order occurs at T{sub N} = 5.5 K at ambient pressure and first increases with pressure up to P {approx} 1.5 GPa, then decreases with further applied pressure up to 3.12 GPa. Another feature, attributed to superconductivity, is observed at 1 K at 1 GPa in the specific heat that grows in magnitude and increases to 2.1 K when the magnetism is weak at 3.12 GPa. Therefore, CePt{sub 2}In{sub 7} displays an evolution with pressure and a coexistence of magnetism and superconductivity that is remarkably similar to that of the heavy fermion superconductor CeRhIn{sub 5}.

  2. Homometallic and Heterometallic Antiferromagnetic Rings: Magnetic Properties Studied by Nuclear Magnetic Resonance

    Energy Technology Data Exchange (ETDEWEB)

    Casadei, Cecilia [Univ. of Pavia (Italy)

    2011-01-01

    The aim of the present thesis is to investigate the local magnetic properties of homometallic Cr8 antiferromagnetic (AFM) ring and the changes occurring by replacing one Cr3+ ion with diamagnetic Cd2+ (Cr7Cd) and with Ni2+ (Cr7Ni). In the heterometallic ring a redistribution of the local magnetic moment is expected in the low temperature ground state. We have investigated those changes by both 53Cr-NMR and 19F-NMR. We have determined the order of magnitude of the transferred hyperfine coupling constant 19F - M+ where M+ = Cr3+, Ni2+ in the different rings. This latter result gives useful information about the overlapping of the electronic wavefunctions involved in the coordinative bond.

  3. Critical point for the canted antiferromagnetic to ferromagnetic phase transition at charge neutrality in bilayer graphene

    Science.gov (United States)

    Pezzini, S.; Cobaleda, C.; Piot, B. A.; Bellani, V.; Diez, E.

    2014-09-01

    We report on magnetotransport measurements up to 30 T performed on a bilayer graphene Hall bar, enclosed by two thin hexagonal boron nitride flakes. In the quantum Hall regime, our high-mobility sample exhibits an insulating state at the neutrality point which evolves into a metallic phase when a strong in-plane field is applied, as expected for a transition from a canted antiferromagnetic to a ferromagnetic spin-ordered phase. We individuate a temperature-independent crossing in the four-terminal resistance as a function of the total magnetic field, corresponding to the critical point of the transition. We show that the critical field scales linearly with the perpendicular component of the field, as expected from the underlying competition between the Zeeman energy and interaction-induced anisotropies. A clear scaling of the resistance is also found and a universal behavior is proposed in the vicinity of the transition.

  4. Terahertz time-domain spectroscopy of magnons in antiferromagnetic MnF2(Conference Presentation)

    Science.gov (United States)

    Bristow, Alan D.; Bas, Derek A.; Borisov, Pavel; Lederman, David

    2017-02-01

    Antiferromagnets are an important class of ordered spin systems, common in spintronic applications and providing a testbed for studying magnetism. Recently, the injection of magnons - coherent spin waves - has been explored by broadband terahertz pulses in antoferromagnets, such as MnO. Here, terahertz time-domain spectroscopy is used to detect magnon resonances in MnF2, which is a model antiferromagnet with uniaxial anisotropy and a Néel temperature of 67 K. Temperature dependence of a one-magnon resonances is examined from 5 K to 70 K. The center frequency of the one-magnon is recorded below the Néel temperature and fit to a Brillouin function. It is found that the degree of correlation between neighboring spins is j = 1.1. Namely, a weak correlation and appropriately modeled by mean-field theory befitting this simple system. From low temperature to room temperature, a two-magnon resonance is observed to broaden and strengthen as the temperature increases. Two-magnon modes arise due to zone-edge magnons being stimulated with -k and +k momenta and do not require magnetic ordering. Over this same temperature range, THz transients are used to monitor the time-of flight through the crystal, the refractive index, the internal energy and the heat capacity. Overall these quantities decrease with decreasing temperature, with behavior that falls into three regimes: a thermal dominated region above the Néel temperature, a magnetic regime below the Néel temperature; and a hyperfine interaction region at temperatures below 6 K. The latter is the first direct observation of the hyperfine interaction using terahertz time-domain spectroscopy.

  5. Optical Signatures of Antiferromagnetic Ordering of Fermionic Atoms in an Optical Lattice

    Directory of Open Access Journals (Sweden)

    Francisco Cordobes Aguilar

    2014-09-01

    Full Text Available We show how off-resonant light scattering can provide quantitative information on antiferromagnetic ordering of a two-species fermionic atomic gas in a tightly-confined two-dimensional optical lattice. We analyze the emerging magnetic ordering of atoms in the mean-field and in random phase approximations and show how the many-body static and dynamic correlations, evaluated in the standard Feynman-Dyson perturbation series, can be detected in the scattered light signal. The staggered magnetization reveals itself in the magnetic Bragg peaks of the individual spin components. These magnetic peaks, however, can be considerably suppressed in the absence of a true long-range antiferromagnetic order. The light scattered outside the diffraction orders can be collected by a lens with highly improved signal-to-shot-noise ratio when the diffraction maxima are blocked. The collective and single-particle excitations are identified in the spectrum of the scattered light. We find that the spin-conserving and spin-exchanging atomic transitions convey information on density, longitudinal spin, and transverse spin correlations. The different correlations and scattering processes exhibit characteristic angular distribution profiles for the scattered light, and e.g., the diagnostic signal of transverse spin correlations could be separated from the optical response by the scattering direction, frequency, or polarization. We also analyze the detection accuracy by estimating the number of required measurements, constrained by the heating rate that is determined by inelastic light-scattering events. The imaging technique could be extended to the two-species fermionic states in other regions of the phase diagram where the ground-state properties are still not fully understood.

  6. Microwave susceptibility experiments

    Energy Technology Data Exchange (ETDEWEB)

    McConaghy, C.

    1984-05-29

    In certain experimental environments, systems can be affected or damaged by microwave pulses. I have conducted tests at LLNL to understand the phenomenology of microwave susceptibility of system components and subsystem components. To date, my experiments have concentrated on bipolar transistors, similar to what might be used in discrete analog circuits, and on CMOS RAM chips, which might be used in a computer memory system. I observed a decrease in failure energies for both the transistor and the integrated curcuit as I shortened the microwave pulse width. An S band (2.86 GHz) transmit/receive (T/R) tube has also been tested both at S band and at X band (8.16 GHz). The S band pulse had limitations in rise-time from zero power, which had an effect on the amount of power that could be transmitted through the T/R tube, as much as 0.7% of the incident power passed through the tube. All tests were conducted in closed-waveguide or coax test-fixtures, in contrast to the anechoic chambers utilized by other experimenters. I have used both S band and X band Klystron generators. For very high power (greater than 1 MW), I used an additional pulse-compression cavity at S band. Other subsystem components such as an X band mixer and an X band T/R tube will be tested in the future. 8 references.

  7. [Antimicrobial susceptibility cumulative reports].

    Science.gov (United States)

    Canut-Blasco, Andrés; Calvo, Jorge; Rodríguez-Díaz, Juan Carlos; Martínez-Martínez, Luis

    2016-10-01

    Cumulative reports on antimicrobial susceptibility tests data are important for selecting empirical treatments, as an educational tool in programs on antimicrobial use, and for establishing breakpoints defining clinical categories. These reports should be based on data validated by clinical microbiologists using diagnostic samples (not surveillance samples). In order to avoid a bias derived from including several isolates obtained from the same patient, it is recommended that, for a defined period, only the first isolate is counted. A minimal number of isolates per species should be presented: a figure of >=30 isolates is statistically acceptable. The report is usually presented in a table format where, for each cell, information on clinically relevant microorganisms-antimicrobial agents is presented. Depending on particular needs, multiple tables showing data related to patients, samples, services or special pathogens can be prepared. Copyright © 2015 Elsevier España, S.L.U. and Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica. All rights reserved.

  8. Genetic susceptibility to pancreatic cancer.

    Science.gov (United States)

    Klein, Alison P

    2012-01-01

    Pancreatic cancer is the fourth leading cause of cancer death in both men and women in the United States. However, it has the poorest prognosis of any major tumor type, with a 5-yr survival rate of approximately 5%. Cigarette smoking, increased body mass index, heavy alcohol consumption, and a diagnosis of diabetes mellitus have all been demonstrated to increase risk of pancreatic cancer. A family history of pancreatic cancer has also been associated with increased risk suggesting inherited genetic factors also play an important role, with approximately 5-10% of pancreatic cancer patients reporting family history of pancreatic cancer. While the genetic basis for the majority of the familial clustering of pancreatic cancer remains unclear, several important pancreatic cancer genes have been identified. These consist of high penetrance genes including BRCA2 or PALB2, to more common genetic variation associated with a modest increase risk of pancreatic cancer such as genetic variation at the ABO blood group locus. Recent advances in genotyping and genetic sequencing have accelerated the rate at which novel pancreatic cancer susceptibility genes have been identified with several genes identified within the past few years. This review addresses our current understanding of the familial aggregation of pancreatic cancer, established pancreatic cancer susceptablity genes and how this knowledge informs risk assessment and screening for high-risk families. Copyright © 2011 Wiley Periodicals, Inc.

  9. Genetic Susceptibility to Pancreatic Cancer

    Science.gov (United States)

    Klein, Alison P.

    2013-01-01

    Pancreatic cancer is the fourth leading cause of cancer death in both men and women in the United States. However, it has the poorest prognosis of any major tumor type, with a 5-yr survival rate of approximately 5%. Cigarette smoking, increased body mass index, heavy alcohol consumption, and a diagnosis of diabetes mellitus have all been demonstrated to increase risk of pancreatic cancer. A family history of pancreatic cancer has also been associated with increased risk suggesting inherited genetic factors also play an important role, with approximately 5–10% of pancreatic cancer patients reporting family history of pancreatic cancer. While the genetic basis for the majority of the familial clustering of pancreatic cancer remains unclear, several important pancreatic cancer genes have been identified. These consist of high penetrance genes including BRCA2 or PALB2, to more common genetic variation associated with a modest increase risk of pancreatic cancer such as genetic variation at the ABO blood group locus. Recent advances in genotyping and genetic sequencing have accelerated the rate at which novel pancreatic cancer susceptibility genes have been identified with several genes identified within the past few years. This review addresses our current understanding of the familial aggregation of pancreatic cancer, established pancreatic cancer susceptablity genes and how this knowledge informs risk assessment and screening for high-risk families. PMID:22162228

  10. Magnetic susceptibility of multiferroics and chemical ordering

    Czech Academy of Sciences Publication Activity Database

    Maryško, Miroslav; Laguta, Valentyn; Raevski, I. P.; Kuzian, R. O.; Olekhnovich, N.M.; Pushkarev, A.V.; Radyush, Yu.V.; Raevskaya, S. I.; Titov, V.V.; Kubrin, S.P.

    2017-01-01

    Roč. 7, č. 5 (2017), s. 1-6, č. článku 056409. ISSN 2158-3226 R&D Projects: GA ČR GA13-11473S Institutional support: RVO:68378271 Keywords : multiferroic * spin glass * antiferromagnetic * ferroelectrics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.568, year: 2016

  11. [Antimicrobial susceptibility in Chile 2012].

    Science.gov (United States)

    Cifuentes-D, Marcela; Silva, Francisco; García, Patricia; Bello, Helia; Briceño, Isabel; Calvo-A, Mario; Labarca, Jaime

    2014-04-01

    Bacteria antimicrobial resistance is an uncontrolled public health problem that progressively increases its magnitude and complexity. The Grupo Colaborativo de Resistencia, formed by a join of experts that represent 39 Chilean health institutions has been concerned with bacteria antimicrobial susceptibility in our country since 2008. In this document we present in vitro bacterial susceptibility accumulated during year 2012 belonging to 28 national health institutions that represent about 36% of hospital discharges in Chile. We consider of major importance to report periodically bacteria susceptibility so to keep the medical community updated to achieve target the empirical antimicrobial therapies and the control measures and prevention of the dissemination of multiresistant strains.

  12. Individual differences in susceptibility to inattentional blindness.

    Science.gov (United States)

    Seegmiller, Janelle K; Watson, Jason M; Strayer, David L

    2011-05-01

    Inattentional blindness refers to the finding that people do not always see what appears in their gaze. Though inattentional blindness affects large percentages of people, it is unclear if there are individual differences in susceptibility. The present study addressed whether individual differences in attentional control, as reflected by variability in working memory capacity, modulate susceptibility to inattentional blindness. Participants watched a classic inattentional blindness video (Simons & Chabris, 1999) and were instructed to count passes among basketball players, wherein 58% noticed the unexpected: a person wearing a gorilla suit. When participants were accurate with their pass counts, individuals with higher working memory capacity were more likely to report seeing the gorilla (67%) than those with lesser working memory capacity (36%). These results suggest that variability in attentional control is a potential mechanism underlying the apparent modulation of inattentional blindness across individuals.

  13. Crystal structure and physical properties of conducting molecular antiferromagnets with a halogen-substituted donor: (EDO-TTFBr2)2FeX4 (X = Cl, Br).

    Science.gov (United States)

    Miyazaki, A; Yamazaki, H; Aimatsu, M; Enoki, T; Watanabe, R; Ogura, E; Kuwatani, Y; Iyoda, M

    2007-04-16

    The crystal structure and physical properties of radical ion salts (EDO-TTFBr2)2FeX4 (X = Cl, Br) based on halogen-substituted organic donor and magnetic anions are investigated, including the comparison with the isomorphous compounds (EDO-TTFBr2)2GaX4 with nonmagnetic anions. The crystal structure of these four salts consists of uniformly stacked donor molecules and tetrahedral counter anions, and the Br substituents of the donor molecules are connected to halide ligands of anions with remarkably short intermolecular atomic distances. These salts show metallic behavior around room temperature and undergo a spin-density-wave transition in the low-temperature range, as confirmed with the divergence of the electron spin resonance (ESR) line width. Although close anion-anion contacts are absent in these salts, the FeCl4 salt undergoes an antiferromagnetic transition at TN = 4.2 K, and the FeBr4 salt shows successive magnetic transitions at TN = 13.5 K and TC2 = 8.5 K with a helical spin structure as a candidate for the ground state of the d-electron spins. The magnetoresistance of the FeCl4 salt shows stepwise anomalies, which are explained qualitatively using a pi-d interaction-based frustrated spin system model composed of the donor pi-electron and the anion d-electron spins. Although on the ESR spectra of the FeX4 salts signals from the pi- and d-electron spins are separately observed, the line width of the pi-electron spins broadens under the temperature where the susceptibility deviates from the Curie-Weiss behavior, showing the presence of the pi-d interaction.

  14. Crystal fields, disorder, and antiferromagnetic short-range order in (Yb{sub 0.24}Sn{sub 0.76})Ru

    Energy Technology Data Exchange (ETDEWEB)

    Klimczuk, T; Wang, C H; Lawrence, J M; Xu, Q; Durakiewicz, T; Ronning, F; Llobet, A; Trouw, F; Kurita, N; Tokiwa, Y; Lee, Han-oh; Booth, C H; Gardner, J S; Bauer, E D; Joyce, J J; Zandbergen, H W; Movshovich, R; Cava, R J; Thompson, J D

    2011-07-18

    We report extensive measurements on a new compound (Yb{sub 0.24}Sn{sub 0.76})Ru that crystallizes in the cubic CsCl structure. Valence band photoemission and L{sub 3} x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb{sup 3+} is split by the crystalline electric field (CEF) into a Γ{sub 7} doublet ground state and a Γ{sub 8} quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a Γ{sub 6} excited state resides at 32 meV; however, the Γ{sub 8}/Γ{sub 6} transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K, there is a peak in specific heat that is too broad to represent a magnetic phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand, this peak also is too narrow to represent the Kondo effect in the Γ{sub 7} ground state doublet. On the basis of the field-dependence of the specific heat, we argue that antiferromagnetic shortrange order (possibly co-existing with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.

  15. pso.ATION AND ANTIMICROBIAL SUSCEPTIBILITY

    African Journals Online (AJOL)

    isolates vere made using standard methods, Antibiotic susceptibility tests against commonly prescribed ... Acute otitis media is rapid with short .... sensitivity tests. Antimicrobial susceptibility tests: The antimicrobial susceptibility patterns of major Gram positive and negative bacterial isolates obtained from clinical specimens.

  16. Susceptibility to COPD: differential proteomic profiling after acute smoking.

    Directory of Open Access Journals (Sweden)

    Lorenza Franciosi

    Full Text Available Cigarette smoking is the main risk factor for COPD (Chronic Obstructive Pulmonary Disease, yet only a subset of smokers develops COPD. Family members of patients with severe early-onset COPD have an increased risk to develop COPD and are therefore defined as "susceptible individuals". Here we perform unbiased analyses of proteomic profiles to assess how "susceptible individuals" differ from age-matched "non-susceptible individuals" in response to cigarette smoking. Epithelial lining fluid (ELF was collected at baseline and 24 hours after smoking 3 cigarettes in young individuals susceptible or non-susceptible to develop COPD and older subjects with established COPD. Controls at baseline were older healthy smoking and non-smoking individuals. Five samples per group were pooled and analysed by stable isotope labelling (iTRAQ in duplicate. Six proteins were selected and validated by ELISA or immunohistochemistry. After smoking, 23 proteins increased or decreased in young susceptible individuals, 7 in young non-susceptible individuals, and 13 in COPD in the first experiment; 23 proteins increased or decreased in young susceptible individuals, 32 in young non-susceptible individuals, and 11 in COPD in the second experiment. SerpinB3 and Uteroglobin decreased after acute smoke exposure in young non-susceptible individuals exclusively, whereas Peroxiredoxin I, S100A9, S100A8, ALDH3A1 (Aldehyde dehydrogenase 3A1 decreased both in young susceptible and non-susceptible individuals, changes being significantly different between groups for Uteroglobin with iTRAQ and for Serpin B3 with iTRAQ and ELISA measures. Peroxiredoxin I, SerpinB3 and ALDH3A1 increased in COPD patients after smoking. We conclude that smoking induces a differential protein response in ELF of susceptible and non-susceptible young individuals, which differs from patients with established COPD. This is the first study applying unbiased proteomic profiling to unravel the underlying

  17. Hypnotic susceptibility and dream characteristics.

    Science.gov (United States)

    Zamore, N; Barrett, D

    1989-11-01

    This study examined the relationship of hypnotic susceptibility to a variety of dream characteristics and types of dream content. A Dream Questionnaire was constructed synthesizing Gibson's dream inventory and Hilgard's theoretical conceptions of hypnosis. Employing the Harvard Group Scale of Hypnotic Susceptibility and the Field Inventory for evaluating hypnotic response, several dream dimensions correlated significantly with hypnotizability. For subjects as a whole, the strongest correlates were the frequency of dreams which they believed to be precognitive and out-of-body dreams. Ability to dream on a chosen topic also correlated significantly with hypnotic susceptibility for both genders. For females only, there was a negative correlation of hypnotic susceptibility to flying dreams. Absorption correlated positively with dream recall, ability to dream on a chosen topic, reports of conflict resolution in dreams, creative ideas occurring in dreams, amount of color in dreams, pleasantness of dreams, bizarreness of dreams, flying dreams and precognitive dreams.

  18. 29 CFR 785.45 - Suggestion systems.

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 3 2010-07-01 2010-07-01 false Suggestion systems. 785.45 Section 785.45 Labor Regulations..., Medical Attention, Civic and Charitable Work, and Suggestion Systems § 785.45 Suggestion systems... general suggestion system is not working time, but if employees are permitted to work on suggestions...

  19. Frustration-induced one-dimensionality in the isosceles triangular antiferromagnetic lattice of δ -(EDT-TTF-CONMe2)2AsF6

    Science.gov (United States)

    Náfrádi, B.; Antal, Á.; Fehér, T.; Kiss, L. F.; Mézière, C.; Batail, P.; Forró, L.; Jánossy, A.

    2016-11-01

    The 1 /4 -filled organic compound, δ -(EDT-TTF-CONMe2)2AsF6 is a frustrated two-dimensional triangular magnetic system as shown by high-frequency (111.2 and 222.4 GHz) electron spin resonance (ESR) and structural data in the literature. The material gradually orders antiferromagnetically below 40 K, but some magnetically disordered domains persist down to 4 K. We propose that in defect free regions frustration prevents true magnetic order down to at least 4 K in spite of the large first- and second-neighbor exchange interactions along chains and between chains, respectively. The antiferromagnetic (AFM) order gradually developing below 40 K nucleates around structural defects that locally cancel frustration. Two antiferromagnetic resonance modes mapped in the principal planes at 4 K are assigned to the very weakly interacting one-dimensional molecular chains in antiferromagnetic regions.

  20. A separation of antiferromagnetic spin motion modes in the training effect of exchange biased Co/CoO film with in-plane anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Wu, R. [State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS (United Kingdom); Yun, C.; Ding, S. L.; Wen, X.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Du, H. L. [State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Yang, J. B., E-mail: jbyang@pku.edu.cn [State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100871 (China)

    2016-08-07

    The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n{sup −1/2} function. A larger CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.

  1. Ancestral susceptibility to colorectal cancer

    Czech Academy of Sciences Publication Activity Database

    Huhn, S.; Pardini, Barbara; Naccarati, Alessio; Vodička, Pavel (ed.); Hemminki, K.; Försti, A.

    2012-01-01

    Roč. 27, č. 2 (2012), s. 197-204 ISSN 0267-8357 R&D Projects: GA ČR GA310/07/1430; GA ČR GAP304/10/1286 Grant - others:EU FP7(XE) HEALTH-F4-2007-200767 Institutional research plan: CEZ:AV0Z50390512 Keywords : cancer susceptibility * molecular epidemiology * genetic susceptibility Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 3.500, year: 2012

  2. Dynamic scaling of the restoration of rotational symmetry in Heisenberg quantum antiferromagnets

    Science.gov (United States)

    Weinberg, Phillip; Sandvik, Anders W.

    2017-08-01

    We apply imaginary-time evolution with the operator e-τ H to study relaxation dynamics of gapless quantum antiferromagnets described by the spin-rotation-invariant Heisenberg Hamiltonian H . Using quantum Monte Carlo simulations to obtain unbiased results, we propagate an initial state with maximal order parameter msz (the staggered magnetization) in the z spin direction and monitor the expectation value 〈ms〉 as a function of imaginary time τ . Results for different system sizes (lengths) L exhibit an initial essentially size independent relaxation of 〈ms〉 toward its value in the infinite-size spontaneously symmetry broken state, followed by a strongly size dependent final decay to zero when the O (3 ) rotational symmetry of the order parameter is restored. We develop a generic finite-size scaling theory that shows the relaxation time diverges asymptotically as Lz, where z is the dynamic exponent of the low-energy excitations. We use the scaling theory to develop a practical way of extracting the dynamic exponent from the numerical finite-size data, systematically eliminating scaling corrections. We apply the method to spin-1 /2 Heisenberg antiferromagnets on two different lattice geometries: the standard two-dimensional (2D) square lattice and a site-diluted 2D square lattice at the percolation threshold. In the 2D case we obtain z =2.001 (5 ) , which is consistent with the known value z =2 , while for the site-diluted lattice we find z =3.90 (1 ) or z =2.056 (8 ) Df , where Df=91 /48 is the fractal dimensionality of the percolating system. This is an improvement on previous estimates of z ≈3.7 . The scaling results also show a fundamental difference between the two cases; for the 2D square lattice, the data can be collapsed onto a common scaling function even when 〈ms〉 is relatively large, reflecting the Anderson tower of quantum rotor states with a common dynamic exponent z =2 . For the diluted 2D square lattice, the scaling works well only for

  3. Temperature controlled motion of an antiferromagnet- ferromagnet interface within a dopant-graded FeRh epilayer

    Directory of Open Access Journals (Sweden)

    C. Le Graët

    2015-04-01

    Full Text Available Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications.

  4. Magnetic excitation spectrum of the square lattice S=1/2 Heisenberg antiferromagnet K2V3O8

    DEFF Research Database (Denmark)

    Lumsden, M.D.; Nagler, S.E.; Sales, B.C.

    2006-01-01

    We have explored the magnetic excitation spectrum of the S=1/2 square lattice Heisenberg antiferromagnet, K2V3O8, using both triple-axis and time-of-flight inelastic neutron scattering. The long-wavelength spin waves are consistent with the previously determined Hamiltonian for this material....... A small energy gap of 72 +/- 9 mu eV is observed at the antiferromagnetic zone center and the near-neighbor exchange constant is determined to be 1.08 +/- 0.03 meV. A finite ferromagnetic interplanar coupling is observed along the crystallographic c axis with a magnitude of J(c)=-0.0036 +/- 0.0006 me...

  5. Two-dimensional Ising behavior in c(2×2) antiferromagnetic Mn and Cr monolayers on Ag(001)

    Science.gov (United States)

    Hanf, M. C.; Krembel, C.; Bolmont, D.; Gewinner, G.

    2003-10-01

    The magnetic order MS(T) is determined as a function of temperature for the c(2×2) antiferromagnetic monolayers of Mn and Cr on Ag(001), using the intensity of the coherent superlattice (1/2,1/2) reflections in low-energy electron diffraction to obtain the sublattice magnetization MS. The data fit the Onsager-Yang theoretical result rather well for the spontaneous magnetization of the plane square lattice in the Ising model with critical temperatures TC≈198 and 462 K for Mn and Cr, respectively. Near TC a fit to a universal power law MS(T)˜(1-T/TC)β confirms the two-dimensional Ising class with β close to 1/8 and indicates the importance of second-order magnetic anisotropy in these two-dimensional antiferromagnets.

  6. Macroscopic quantum coherence and tunneling of an antiferromagnetic nanoparticle in a magnetic field at an arbitrarily directed angle

    Science.gov (United States)

    Lü, Rong; Zhu, Jia-Lin; Wang, Xiao-Bing; Chang, Lee

    1999-08-01

    Based on the two-sublattice model, we investigate the quantum tunneling behaviors of the Néel vector in single-domain antiferromagnetic nanoparticles placed in an external magnetic field at an arbitrarily directed angle in the ZX plane. We consider the magnetocrystalline anisotropy with biaxial, tetragonal, and hexagonal crystal symmetry, respectively. By applying the standard instanton technique in the spin-coherent-state path-integral representation, we calculate the tunneling level splittings, the tunneling rates, and the crossover temperatures in the low barrier limit for three angle ranges of the external applied magnetic field (θH=π/2, πcrossover temperatures depend on the orientation of the external applied magnetic field distinctly, which provides a possible experimental test for macroscopic quantum tunneling and coherence of the Néel vector in nanometer-scale single-domain antiferromagnets.

  7. The comparative study of bulk magneto-phonon and magnetic polaritons of lateral antiferromagnetic superlattices for potential THz applications

    Energy Technology Data Exchange (ETDEWEB)

    Ta, Jin-Xing, E-mail: tajinxing@sina.com; Han, Yu, E-mail: hanyu5214@163.com; Lan, Cheng

    2016-02-01

    Bulk magneto-phonon and magnetic polaritons of lateral antiferromagnetic superlattices for potential THz applications have been investigated in the framework of the effective medium theory. The dispersion relations applied for the system are displayed. In contrast with lateral FeF{sub 2}/SiO{sub 2} superlattice, some fascinating polariton modes with negative group velocity signifying photonic band gap scenarios and attractive optical properties are observed from the numerical results presented with the example, lateral FeF{sub 2}/TlBr superlattice. - Highlights: • Bulk magneto-phonon and magnetic polaritons in the THz frequency regime are discussed. • Negative refraction at certain frequencies is predicted in lateral FeF{sub 2}/TlBr superlattice. • This appealing nature can be adjusted by the applied magnetic field and the antiferromagnetic volume fraction.

  8. Observation of new magnetic ground state in frustrated quantum antiferromagnet spin-liquid system Cs2CuCl4

    Science.gov (United States)

    Kim, Hyeong-Jin; Haines, C. R. S.; Liu, C.; Chun, Sae Hwan; Kim, Kee Hoon; Yi, H. T.; Cheong, Sang-Wook; Saxena, Siddharth S.

    2017-08-01

    Cs2CuCl4 is known to possess a quantum spin-liquid phase with antiferromagnetic interaction below 2.8 K. We report the observation of a new metastable magnetic phase of the triangular frustrated quantum spin system Cs2CuCl4 induced by the application of hydrostatic pressure. We measured the magnetic properties of Cs2CuCl4 following the application and release of pressure after 3 days. We observed a previously unknown ordered magnetic phase with a transition temperature of 9 K. Furthermore, the recovered sample with new magnetic ground state possesses an equivalent crystal structure to the uncompressed one with antiferromagnetic quantum spinliquid phase.

  9. High-resolution resonant inelastic extreme ultraviolet scattering from orbital and spin excitations in a Heisenberg antiferromagnet

    Science.gov (United States)

    Caretta, Antonio; Dell'Angela, Martina; Chuang, Yi-De; Kalashnikova, Alexandra M.; Pisarev, Roman V.; Bossini, Davide; Hieke, Florian; Wurth, Wilfried; Casarin, Barbara; Ciprian, Roberta; Parmigiani, Fulvio; Wexler, Surge; Wray, L. Andrew; Malvestuto, Marco

    2017-11-01

    We report a high-resolution resonant inelastic extreme ultraviolet (EUV) scattering study of the quantum Heisenberg antiferromagnet KCoF3. By tuning the EUV photon energy to the cobalt M23 edge, a complete set of low-energy 3 d spin-orbital excitations is revealed. These low-lying electronic excitations are modeled using an extended multiplet-based mean-field calculation to identify the roles of lattice and magnetic degrees of freedom in modifying the resonant inelastic x-ray scattering (RIXS) spectral line shape. We have demonstrated that the temperature dependence of RIXS features upon the antiferromagnetic ordering transition enables us to probe the energetics of short-range spin correlations in this material.

  10. Neutron scattering studies of two-dimensional antiferromagnetic spin fluctuations in insulating and superconducting S = ½ systems

    DEFF Research Database (Denmark)

    Christensen, Niels Bech

    Time-of-flight and polarized triple axis neutron scattering is used to probe the spin excitations of Cu(DCOO)_2_·_4D_2O and La_2_-_xSr_xCuO_4. The first part of the thesis contains an investigation of the excitation spectrum of the square lattice S = 1/2Heisenberg antiferromagnet Cu(DCOO)_2_·_4D_...

  11. Antiferromagnetic order driven chiral topological spin density waves on the repulsive Haldane-Hubbard model on square lattices.

    Science.gov (United States)

    Wu, Ya-Jie; Li, Ning; He, Jing; Kou, Su-Peng

    2016-03-23

    In this paper, based on mean-field approach and random-phase-approximation, we study the magnetic properties of the repulsive Haldane-Hubbard model on a square lattice. We find antiferromagnetic order driven topological spin density waves beyond Landau's symmetry-breaking paradigm, for which the effective low energy physics is determined by Chern-Simons-Hopf gauge field theories with different K matrices.

  12. Antiferromagnetic geometric frustration under the influence of the next-nearest-neighbor interaction. An exactly solvable model

    Science.gov (United States)

    Jurčišinová, E.; Jurčišin, M.

    2018-02-01

    The influence of the next-nearest-neighbor interaction on the properties of the geometrically frustrated antiferromagnetic systems is investigated in the framework of the exactly solvable antiferromagnetic spin- 1 / 2 Ising model in the external magnetic field on the square-kagome recursive lattice, where the next-nearest-neighbor interaction is supposed between sites within each elementary square of the lattice. The thermodynamic properties of the model are investigated in detail and it is shown that the competition between the nearest-neighbor antiferromagnetic interaction and the next-nearest-neighbor ferromagnetic interaction changes properties of the single-point ground states but does not change the frustrated character of the basic model. On the other hand, the presence of the antiferromagnetic next-nearest-neighbor interaction leads to the enhancement of the frustration effects with the formation of additional plateau and single-point ground states at low temperatures. Exact expressions for magnetizations and residual entropies of all ground states of the model are found. It is shown that the model exhibits various ground states with the same value of magnetization but different macroscopic degeneracies as well as the ground states with different values of magnetization but the same value of the residual entropy. The specific heat capacity is investigated and it is shown that the model exhibits the Schottky-type anomaly behavior in the vicinity of each single-point ground state value of the magnetic field. The formation of the field-induced double-peak structure of the specific heat capacity at low temperatures is demonstrated and it is shown that its very existence is directly related to the presence of highly macroscopically degenerated single-point ground states in the model.

  13. Strain driven anisotropic magnetoresistance in antiferromagnetic La$_{0.4}$Sr$_{0.6}$MnO$_{3}$

    OpenAIRE

    Wong, AT; Beekman, C.; Guo, H.; W. Siemons; Gai, Z.; Arenholz, E.; Takamura, Y.; Ward, TZ

    2014-01-01

    We investigate the effects of strain on antiferromagnetic (AFM) single crystal thin films of La 1-x Sr x MnO 3 (x = 0.6). Nominally unstrained samples have strong magnetoresistance with anisotropic magnetoresistances (AMR) of up to 8%. Compressive strain suppresses magnetoresistance but generates AMR values of up to 63%. Tensile strain presents the only case of a metal-insulator transition and demonstrates a previously unreported AMR behavior. In all three cases, we find evidence of magnetic...

  14. Magnetization process and magnetocaloric effect in geometrically frustrated Ising antiferromagnet and spin ice models on a `Star of David' nanocluster

    OpenAIRE

    Žukovič, M.; Semjan, M.

    2017-01-01

    Magnetic and magnetocaloric properties of geometrically frustrated antiferromagnetic Ising (IA) and ferromagnetic spin ice (SI) models on a nanocluster with a `Star of David' topology, including next-nearest-neighbor (NNN) interactions, are studied by an exact enumeration. In an external field applied in characteristic directions of the respective models, depending on the NNN interaction sign and magnitude, the ground state magnetization of the IA model is found to display up to three interme...

  15. Possible Correlation Between Stripe-Like Antiferromagnetic Spin Fluctuations and Superconductivity in ThFeAsN

    Science.gov (United States)

    Kumar, Jagdish

    2017-08-01

    The recently invented ThFeAsN superconductor, belonging to the family of Fe-based superconductors, has been studied using ab initio density functional theory. Our calculations demonstrate that the electronic structure of this superconductor is similar to that of other Fe-based superconductors with computed magnetic ground state showing strong dependence on atomic positions. Using relaxed atomic positions, the single- and double-stripe magnetic states are found to be energetically close to each other, which may lead to stripe-like antiferromagnetic spin fluctuations. We speculate that such energetic degeneracy among two antiferromagnetic structures may be an ideal condition for strong stripe-like antiferromagnetic spin fluctuations, which may be playing a key role in obtaining high transition temperature of 30 K. Fixed spin moment calculations demonstrate the possibility of local minima for magnetic states in ThFeAsN. The absence of long-range ordering in ThFeAsN may be due to presence of such local minima.

  16. Genetic architecture of intrinsic antibiotic susceptibility.

    Directory of Open Access Journals (Sweden)

    Hany S Girgis

    2009-05-01

    Full Text Available Antibiotic exposure rapidly selects for more resistant bacterial strains, and both a drug's chemical structure and a bacterium's cellular network affect the types of mutations acquired.To better characterize the genetic determinants of antibiotic susceptibility, we exposed a transposon-mutagenized library of Escherichia coli to each of 17 antibiotics that encompass a wide range of drug classes and mechanisms of action. Propagating the library for multiple generations with drug concentrations that moderately inhibited the growth of the isogenic parental strain caused the abundance of strains with even minor fitness advantages or disadvantages to change measurably and reproducibly. Using a microarray-based genetic footprinting strategy, we then determined the quantitative contribution of each gene to E. coli's intrinsic antibiotic susceptibility. We found both loci whose removal increased general antibiotic tolerance as well as pathways whose down-regulation increased tolerance to specific drugs and drug classes. The beneficial mutations identified span multiple pathways, and we identified pairs of mutations that individually provide only minor decreases in antibiotic susceptibility but that combine to provide higher tolerance.Our results illustrate that a wide-range of mutations can modulate the activity of many cellular resistance processes and demonstrate that E. coli has a large mutational target size for increasing antibiotic tolerance. Furthermore, the work suggests that clinical levels of antibiotic resistance might develop through the sequential accumulation of chromosomal mutations of small individual effect.

  17. Phase processing for quantitative susceptibility mapping of regions with large susceptibility and lack of signal.

    Science.gov (United States)

    Fortier, Véronique; Levesque, Ives R

    2017-11-11

    Phase processing impacts the accuracy of quantitative susceptibility mapping (QSM). Techniques for phase unwrapping and background removal have been proposed and demonstrated mostly in brain. In this work, phase processing was evaluated in the context of large susceptibility variations (Δχ) and negligible signal, in particular for susceptibility estimation using the iterative phase replacement (IPR) algorithm. Continuous Laplacian, region-growing, and quality-guided unwrapping were evaluated. For background removal, Laplacian boundary value (LBV), projection onto dipole fields (PDF), sophisticated harmonic artifact reduction for phase data (SHARP), variable-kernel sophisticated harmonic artifact reduction for phase data (V-SHARP), regularization enabled sophisticated harmonic artifact reduction for phase data (RESHARP), and 3D quadratic polynomial field removal were studied. Each algorithm was quantitatively evaluated in simulation and qualitatively in vivo. Additionally, IPR-QSM maps were produced to evaluate the impact of phase processing on the susceptibility in the context of large Δχ with negligible signal. Quality-guided unwrapping was the most accurate technique, whereas continuous Laplacian performed poorly in this context. All background removal algorithms tested resulted in important phase inaccuracies, suggesting that techniques used for brain do not translate well to situations where large Δχ and no or low signal are expected. LBV produced the smallest errors, followed closely by PDF. Results suggest that quality-guided unwrapping should be preferred, with PDF or LBV for background removal, for QSM in regions with large Δχ and negligible signal. This reduces the susceptibility inaccuracy introduced by phase processing. Accurate background removal remains an open question. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  18. Solitary Magnons in the S=5/2 Antiferromagnet CaFe_{2}O_{4}.

    Science.gov (United States)

    Stock, C; Rodriguez, E E; Lee, N; Green, M A; Demmel, F; Ewings, R A; Fouquet, P; Laver, M; Niedermayer, Ch; Su, Y; Nemkovski, K; Rodriguez-Rivera, J A; Cheong, S-W

    2016-07-01

    CaFe_{2}O_{4} is a S=5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c-axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ∼1  ns at the onset of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions ∼1-2 c-axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A+B orders as well as localization of spin excitations in a classical magnet.

  19. Electronic control of interface ferromagnetic order and exchange-bias in paramagnetic-antiferromagnetic epitaxial bilayers.

    Science.gov (United States)

    Pandey, Parul; Das, Tanmay; Rana, Rakesh; Parmar, Jayesh B; Bhattacharyya, Somnath; Rana, Dhanvir Singh

    2015-02-21

    The hetero-epitaxially engineered magnetic phases, formed due to entanglement of the spin, charge and lattice degrees of freedom, at the atomically sharp interfaces of complex oxide heterostructures are indispensable for devising multifunctional devices. In the quest for novel and superior spintronics functionalities, we have explored the interface magnetism in the epitaxial bilayer of atypical magnetic and electronic states, i.e., of paramagnetic metallic and antiferromagnetic (AFM) insulating phases. In this framework, we observe an unusually strong ferromagnetic order and large exchange-bias fields generated at the interface of the bilayers of metallic CaRuO3 and AFM insulating manganite. The magnetic moment of the interface ferromagnetic order increases linearly with increasing thickness (7-90 nm) of the metallic CaRuO3 layer. This linear scaling signifying an electronic (non-magnetic) control of the interface magnetism and a non-monotonic dependence of the exchange-bias on metallic layers evolve as novel spintronics attributes in atypical bilayers.

  20. Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

    KAUST Repository

    Manchon, Aurelien

    2018-01-29

    Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current-induced spin-orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching of ferromagnetic as well as antiferromagnetic structures. The manipulation of magnetic order, domain walls and skyrmions by spin-orbit torques provides evidence of the microscopic interactions between charge and spin in a variety of materials and opens novel strategies to design spintronic devices with potentially high impact in data storage, nonvolatile logic, and magnonic applications. This paper reviews recent progress in the field of spin-orbitronics, focusing on theoretical models, material properties, and experimental results obtained on bulk noncentrosymmetric conductors and multilayer heterostructures, including metals, semiconductors, and topological insulator systems. Relevant aspects for improving the understanding and optimizing the efficiency of nonequilibrium spin-orbit phenomena in future nanoscale devices are also discussed.

  1. Antiferromagnetic Spin Coupling between Rare Earth Adatoms and Iron Islands Probed by Spin-Polarized Tunneling

    Science.gov (United States)

    Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; Fuente, César De La; Arnaudas, José Ignacio

    2015-09-01

    High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths.

  2. Tuning frustrated antiferromagnetism in intermetallic AFe{sub 4}X{sub 2} systems

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Katharina [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Institute of Solid State Physics, Dresden University of Technology, Dresden (Germany); Mufti, Nandang; Bergmann, Christoph; Kraft, Inga; Rosner, Helge; Geibel, Christoph [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Goltz, Til; Klauss, Hans-Henning [Institute of Solid State Physics, Dresden University of Technology, Dresden (Germany); Woike, Theo [Institute for Structural Physics, Dresden University of Technology, Dresden (Germany)

    2013-07-01

    Magnetic systems with reduced dimensionality or frustration are attracting strong interest because these features lead to an increase of quantum fluctuations which often results in unusual, very interesting properties. Here we present a detailed study of the intermetallic AFe{sub 4}X{sub 2} compounds (A=Sc,Y,Lu,Zr; X=Si,Ge) crystallizing in the ZrFe{sub 4}Si{sub 2} structure type in which the Fe-sublattice is formed by chains of edge-linked tetrahedra. We synthesized polycrystalline samples of all these compounds and investigated their magnetic, thermodynamic, structural and transport properties. Our results indeed evidence this family of compounds to cover the whole regime from frustrated antiferromagnetic (AFM) order up to the quantum critical point separating the AFM ground state from the paramagnetic ground state. All compounds with trivalent A elements show frustrated AFM order. Replacement of trivalent A by tetravalent Zr shifts the system towards an unstable magnetic state. Since YFe{sub 4}Si{sub 2} and ZrFe{sub 4}Si{sub 2} present peculiar features, we also studied the influence of different annealing conditions and slight off-stoichiometry on their unusual properties.

  3. The sensitivity of surface polaritons in LHM-antiferromagnetic waveguide sensors

    Energy Technology Data Exchange (ETDEWEB)

    El-Khozondar, Hala J., E-mail: hkhozondar@iugaza.edu [Electrical Engineering Department, Islamic University, P.O.Box 108, Gaza, Palestine (Country Unknown); Al-Sahhar, Zeyad I., E-mail: z_alsahhar@yahoo.com [Physics Department, Al-Aqsa University, Gaza, Palestine (Country Unknown); Shabat, Mohamad M., E-mail: shabat@iugaza.edu.ps [Physics Department, Islamic University, Gaza, Palestine (Country Unknown)

    2014-11-15

    A three-layer waveguide structure sensor consisting of LHMs film surrounded by dielectric cladding and antiferromagnetic substrate is proposed. Left-handed materials (LHMs) known as Metamaterials (MTMs) have simultaneous negative permeability and permittivity. The dispersion relation for the structure is derived for TE modes only. The sensitivity is calculated for surface waves at the interface between LHM film and dielectric layer. Two ranges of frequencies are chosen such that the Voigt permeability, μ{sub v}, is either negative or positive. The sensitivity is proven to be affected by different parameters including the film thickness, LHM parameters, and Voigt permittivity. The results show that the proposed structure is sensitive to small changes in the cladding indicating that the structure is working as a sensor with high sensitivity. The parameters at which maximum sensitivity occur are obtained. - Highlights: • The homogenous sensitivity is used to measure the sensitivity of the structure. • Sensitivity changes as the value of Voigt permittivity, μ{sub v}, changes sign. • The sensitivity is affected by the film thickness and the LHM parameters. • The three-layered sensor has high sensitivity and compact structure. • The parameters at which we achieved maximum sensitivity are obtained.

  4. Deconfined quantum criticality in SU(3) antiferromagnets on the triangular lattice

    Science.gov (United States)

    Pimenov, Dimitri; Punk, Matthias

    2017-05-01

    We propose field theories for a deconfined quantum critical point in SU(3) antiferromagnets on the triangular lattice. In particular we consider the continuous transition between a magnetic, three-sublattice color-ordered phase and a trimerized SU(3) singlet phase. Starting from the magnetically ordered state we derive a critical theory in terms of fractional bosonic degrees of freedom, in close analogy to the well-developed description of the SU(2) Néel—valence bond solid (VBS) transition on the square lattice. Our critical theory consists of three coupled C P2 models and we study its fixed point structure using a functional renormalization group approach in a suitable large N limit. We find a stable critical fixed point and estimate its critical exponents, thereby providing an example of deconfined criticality beyond the universality class of the C PN model. In addition we present a complementary route towards the critical field theory by studying topological defects of the trimerized SU(3) singlet phase.

  5. Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field

    Science.gov (United States)

    Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan

    2012-06-01

    By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field hc = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h behavior of block entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.

  6. Spin wave dynamics in Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Mi, Bin-Zhou, E-mail: mbzfjerry2008@126.com [Department of Basic Curriculum, North China Institute of Science and Technology, Beijing 101601 (China); Department of Physics, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083 (China)

    2016-09-15

    The spin wave dynamics, including the magnetization, spin wave dispersion relation, and energy level splitting, of Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes are systematically calculated by use of the double-time Green’s function method within the random phase approximation. The role of temperature, diameter of the tube, and wave vector on spin wave energy spectrum and energy level splitting are carefully analyzed. There are two categories of spin wave modes, which are quantized and degenerate, and the total number of independent magnon branches is dependent on diameter of the tube, caused by the physical symmetry of nanotubes. Moreover, the number of flat spin wave modes increases with diameter of the tube rising. The spin wave energy and the energy level splitting decrease with temperature rising, and become zero as temperature reaches the critical point. At any temperature, the energy level splitting varies with wave vector, and for a larger wave vector it is smaller. When pb=π, the boundary of first Brillouin zone, spin wave energies are degenerate, and the energy level splittings are zero.

  7. Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field.

    Science.gov (United States)

    Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan

    2012-06-27

    By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h(c) = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.

  8. Field induced spontaneous quasiparticle decay and renormalization of quasiparticle dispersion in a quantum antiferromagnet

    Science.gov (United States)

    Hong, Tao; Qiu, Y.; Matsumoto, M.; Tennant, D. A.; Coester, K.; Schmidt, K. P.; Awwadi, F. F.; Turnbull, M. M.; Agrawal, H.; Chernyshev, A. L.

    2017-01-01

    The notion of a quasiparticle, such as a phonon, a roton or a magnon, is used in modern condensed matter physics to describe an elementary collective excitation. The intrinsic zero-temperature magnon damping in quantum spin systems can be driven by the interaction of the one-magnon states and multi-magnon continuum. However, detailed experimental studies on this quantum many-body effect induced by an applied magnetic field are rare. Here we present a high-resolution neutron scattering study in high fields on an S=1/2 antiferromagnet C9H18N2CuBr4. Compared with the non-interacting linear spin–wave theory, our results demonstrate a variety of phenomena including field-induced renormalization of one-magnon dispersion, spontaneous magnon decay observed via intrinsic linewidth broadening, unusual non-Lorentzian two-peak structure in the excitation spectra and a dramatic shift of spectral weight from one-magnon state to the two-magnon continuum. PMID:28474679

  9. Electric field control of magnetization direction across the antiferromagnetic to ferromagnetic transition.

    Science.gov (United States)

    Zheng, Guohui; Ke, San-Huang; Miao, Maosheng; Kim, Jinwoong; Ramesh, R; Kioussis, Nicholas

    2017-07-14

    Electric-field-induced magnetic switching can lead to a new paradigm of ultra-low power nonvolatile magnetoelectric random access memory (MeRAM). To date the realization of MeRAM relies primarily on ferromagnetic (FM) based heterostructures which exhibit low voltage-controlled magnetic anisotropy (VCMA) efficiency. On the other hand, manipulation of magnetism in antiferromagnetic (AFM) based nanojunctions by purely electric field means (rather than E-field induced strain) remains unexplored thus far. Ab initio electronic structure calculations reveal that the VCMA of ultrathin FeRh/MgO bilayers exhibits distinct linear or nonlinear behavior across the AFM to FM metamagnetic transition depending on the Fe- or Rh-interface termination. We predict that the AFM Fe-terminated phase undergoes an E-field magnetization switching with large VCMA efficiency and a spin reorientation across the metamagnetic transition. In sharp contrast, while the Rh-terminated interface exhibits large out-of-plane (in-plane) MA in the FM (AFM) phase, its magnetization is more rigid to external E-field. These findings demonstrate that manipulation of the AFM Néel-order magnetization direction via purely E-field means can pave the way toward ultra-low energy AFM-based MeRAM devices.

  10. Direct observation of imprinted antiferromagnetic vortex state in CoO/Fe/Ag(001) disks

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J.; Carlton, D.; Park, J. S.; Meng, Y.; Arenholz, E.; Doran, A.; Young, A.T.; Scholl, A.; Hwang, C.; Zhao, H. W.; Bokor, J.; Qiu, Z. Q.

    2010-12-21

    In magnetic thin films, a magnetic vortex is a state in which the magnetization vector curls around the center of a confined structure. A vortex state in a thin film disk, for example, is a topological object characterized by the vortex polarity and the winding number. In ferromagnetic (FM) disks, these parameters govern many fundamental properties of the vortex such as its gyroscopic rotation, polarity reversal, core motion, and vortex pair excitation. However, in antiferromagnetic (AFM) disks, though there has been indirect evidence of the vortex state through observations of the induced FM-ordered spins in the AFM disk, they have never been observed directly in experiment. By fabricating single crystalline NiO/Fe/Ag(001) and CoO/Fe/Ag(001) disks and using X-ray Magnetic Linear Dichroism (XMLD), we show direct observation of the vortex state in an AFM disk of AFM/FM bilayer system. We observe that there are two types of AFM vortices, one of which has no analog in FM structures. Finally, we show that a frozen AFM vortex can bias a FM vortex at low temperature.

  11. Heat switch effect in an antiferromagnetic insulator Co3V2O8

    Science.gov (United States)

    Zhao, X.; Wu, J. C.; Zhao, Z. Y.; He, Z. Z.; Song, J. D.; Zhao, J. Y.; Liu, X. G.; Sun, X. F.; Li, X. G.

    2016-06-01

    We report a heat switch effect in single crystals of an antiferromagnet Co3V2O8, that is, the thermal conductivity (κ) can be changed with magnetic field in an extremely large scale. Due to successive magnetic phase transitions at 12-6 K, the zero-field κ(T ) displays a deep minimum at 6.7 K and rather small magnitude at low temperatures. Both the temperature and field dependencies of κ demonstrate that the phonons are strongly scattered at the regime of magnetic phase transitions. Magnetic field can suppress magnetic scattering effect and significantly recover the phonon thermal conductivity. In particular, a 14 T field along the a axis increases the κ at 7.5 K up to 100 times. For H ∥c , the magnitude of κ can be suppressed down to ˜8% at some field-induced transition and can be enhanced up to 20 times at 14 T. The present results demonstrate that it is possible to design a kind of heat switch in the family of magnetic materials.

  12. Spin-triplet supercurrent in Josephson junctions containing a synthetic antiferromagnet with perpendicular magnetic anisotropy

    Science.gov (United States)

    Glick, Joseph A.; Edwards, Samuel; Korucu, Demet; Aguilar, Victor; Niedzielski, Bethany M.; Loloee, Reza; Pratt, W. P.; Birge, Norman O.; Kotula, P. G.; Missert, N.

    2017-12-01

    We present measurements of Josephson junctions containing three magnetic layers with noncollinear magnetizations. The junctions are of the form S /F'/N /F /N /F″/S , where S is superconducting Nb, F' is either a thin Ni or Permalloy layer with in-plane magnetization, N is the normal metal Cu, F is a synthetic antiferromagnet with magnetization perpendicular to the plane, composed of Pd/Co multilayers on either side of a thin Ru spacer, and F″ is a thin Ni layer with in-plane magnetization. The supercurrent in these junctions decays more slowly as a function of the F -layer thickness than for similar spin-singlet junctions not containing the F' and F″ layers. The slower decay is the prime signature that the supercurrent in the central part of these junctions is carried by spin-triplet pairs. The junctions containing F'= Permalloy are suitable for future experiments where either the amplitude of the critical current or the ground-state phase difference across the junction is controlled by changing the relative orientations of the magnetizations of the F' and F″ layers.

  13. Antiferromagnetic resonance in multiferroic YMnO{sub 3} and LuMnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Kamensky, D.; Ozerov, M.; Cizmar, E.; Wosnitza, J.; Zvyagin, S. [Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden - Rossendorf, 01314 Dresden (Germany)

    2009-07-01

    Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic order. Combining conventional far-infrared Fourier-transform and THz-range free electron laser electron spin resonance (ESR) techniques, magnetic excitations in the hexagonal multiferroic materials YMnO{sub 3} and LuMnO{sub 3} have been studied. In the antiferromagnetically (AFM) ordered phase the gap in the excitation spectrum ({proportional_to}42 and {proportional_to}48 cm{sup -1} for YMnO{sub 3} and LuMnO{sub 3}, respectively) was observed directly. Similar slope of the frequency-field dependences of the AFM resonance modes, {proportional_to} 0.5 cm{sup -1}/T, was found for both compounds. A fine structure of the AFM resonance absorption has been revealed by means of high-resolution ESR techniques, which can be explained taking into account a finite interaction between the neighboring Mn{sup 3+} layers.

  14. Ferromagnetism of Pd(001) substrate induced by antiferromagnetic CoO

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Srijan Kumar, E-mail: sksaha@mpi-halle.mpg.de; Stepanyuk, Valeri S.; Kirschner, Jürgen

    2014-11-14

    Our first-principles study has revealed unexpected spin polarization of the Pd(001) substrate in contact with antiferromagnetic CoO overlayers. We give an evidence that the ferromagnetism of Pd is caused by the zigzag positions of Co atoms with respect to the Pd interface, resulted from the lattice-mismatch driven structural relaxation. Because of the itinerant nature of its 4d electrons, we see that the ferromagnetic properties of Pd are highly sensitive to the local environment and can be enhanced further by increasing the thickness of CoO overlayer film or/and by applying an additional uniaxial pressure along c-axis exerted externally on the bottom layers of the Pd substrate. Our finding provides new functionality for the interfacial moments of the CoO/Pd system, which can be accessed experimentally, e.g., by the magneto-optical Kerr effect (MOKE) or/and by element-resolved X-ray magnetic circular dichroism (XMCD) measurement.

  15. Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures

    Science.gov (United States)

    Nairan, Adeela; Khan, Maaz; Khan, Usman; Iqbal, Munawar; Riaz, Saira; Naseem, Shahzad

    2016-01-01

    In this work MnxCo1−xFe2O4 nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm−1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe2O4) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field. PMID:28335203

  16. Covalent magnetism, exchange interactions and anisotropy of the high temperature layered antiferromagnet MnB₂.

    Science.gov (United States)

    Khmelevskyi, S; Mohn, P

    2012-01-11

    The investigation of the electronic structure and magnetism for the compound MnB(2) with crystal structure type AlB(2) has been revisited to resolve contradictions between various experimental and theoretical results present in the literature. We find that MnB(2) exhibits an interesting example of a Kübler's covalent magnetism (Williams et al 1981 J. Appl. Phys. 52 2069). The covalent magnetism also appears to be the source of some disagreement between the calculated values of the magnetic moments and those given by neutron diffraction experiments. We show that this shortcoming is due to the atomic sphere approximation applied in earlier calculations. The application of the disordered local moment approach and the calculation of the inter-atomic exchange interactions within the Liechtenstein formalism reveal strong local moment antiferromagnetism with a high Néel temperature predicted from Monte Carlo simulations. A fully relativistic band structure calculation and then the application of the torque method yields a strong in-plane anisotropy of the Mn magnetic moments. The agreement of these results with neutron diffraction studies rules out any possible weak itinerant electron magnetism scenarios as proposed earlier for MnB(2).

  17. Superconductivity and charge order near the onset of antiferromagnetism in metals

    Energy Technology Data Exchange (ETDEWEB)

    Gerlach, Max Henner; Trebst, Simon [University of Cologne (Germany); Schattner, Yonathan; Berg, Erez [Weizmann Insitute of Science, Rehovot (Israel)

    2015-07-01

    The quantum-critical transition of a system of itinerant electrons into an antiferromagnetically ordered phase has long been believed to play an important role in the physics of superconductors such as the electron-doped cuprates and the iron pnictides. The complete understanding of this quantum-critical point has remained a key challenge for both analytical and numerical approaches. On the computational side, a numerically exact simulation of such fermionic systems via quantum Monte Carlo studies has long been precluded by the infamous negative sign problem. Only recently a way has been found to set up sign-problem-free simulations of lattice models that realize the universal physics close to this phase transition. Building upon this conceptual work, we introduce further improvements to the Monte Carlo sampling techniques adapted to such a model, allowing us to better understand the properties of the quantum-critical point and the instability towards d-wave-like superconductivity in its vicinity. In addition, we study a competing instability towards a charge-density-wave-like order, which we support by a supplementary interaction. Taken together, our results further improve our understanding of the rich physics of a relatively simple single-band electron model appropriate for the cuprates.

  18. Theoretical prediction of antiferromagnetism in layered perovskite Sr2TcO4

    Science.gov (United States)

    Horvat, Alen; Pourovskii, Leonid; Aichhorn, Markus; Mravlje, Jernej

    2017-05-01

    We theoretically investigate the magnetic properties of Sr2TcO4 , a 4 d transition-metal layered perovskite of the K2NiF4 type with half-filled t2 g states. The effect of local Coulomb repulsion between the t2 g orbitals is included within the density-functional theory (DFT) + U and DFT + dynamical mean-field theory (DMFT) methods. The DFT + DMFT predicts paramagnetic Sr2TcO4 to be close to the Mott insulator-to-metal transition, similarly to the cubic compound SrTcO3. The intersite exchange interactions computed within the DFT + DMFT framework point to a strong antiferromagnetic coupling between the neighboring Tc sites within the layer. We then evaluate the Néel temperature TN within a classical Monte Carlo approach including dipolar interactions, which stabilize the magnetic order in the frustrated K2NiF4 lattice structure. Our approach is validated by applying it to a set of layered and cubic perovskites, for which we obtain TN in fair agreement with experiment. Within the same approach we obtain the TN of Sr2TcO4 to be about 450 K. We explore also the effect of anisotropy in exchange interactions due to spin-orbit coupling. These lead to a somewhat higher transition temperature, 550 K.

  19. Magnetic ground state of the Ising-like antiferromagnet DyScO3

    Science.gov (United States)

    Wu, L. S.; Nikitin, S. E.; Frontzek, M.; Kolesnikov, A. I.; Ehlers, G.; Lumsden, M. D.; Shaykhutdinov, K. A.; Guo, E.-J.; Savici, A. T.; Gai, Z.; Sefat, A. S.; Podlesnyak, A.

    2017-10-01

    We report on the low-temperature magnetic properties of the DyScO3 perovskite, which were characterized by means of single crystal and powder neutron scattering, and by magnetization measurements. Below TN=3.15 K, Dy3 + moments form an antiferromagnetic structure with an easy axis of magnetization lying in the a b plane. The magnetic moments are inclined at an angle of ˜±28∘ to the b axis. We show that the ground-state Kramers doublet of Dy3 + is made up of primarily |±15 /2 〉 eigenvectors and well separated by a crystal field from the first excited state at E1=24.9 meV. This leads to an extreme Ising single-ion anisotropy, M⊥/M∥˜0.05 . The transverse magnetic fluctuations, which are proportional to M⊥2/M∥2 , are suppressed, and only moment fluctuations along the local Ising direction are allowed. We also found that the Dy-Dy dipolar interactions along the crystallographic c axis are two to four times larger than in-plane interactions.

  20. High Faraday effect of antiferromagnetic/ion-crystal photonic crystals in far infrared region

    Science.gov (United States)

    Wang, Xuan-Zhang; Zhao, Yan

    2013-01-01

    The Faraday effect of one-dimensional antiferromagnetic/ion-crystal photonic crystals (AF/IC PCs) is investigated. In numerical calculation, AF layers are FeF2 and IC layers are of IV-VI semiconductor. A valuable geometry with higher Faraday effect is found, where an incident electromagnetic wave normally illuminates the lateral surface of such a PC and the external field and AF anisotropy axis both are pointed along the wave-vector. From the numerical results based on several relevant PCs, we conclude that the FeF2/PbSe PC possesses the highest Faraday effect. Although the effect originates from AF layers and is influenced by the PC anisotropy, the rotation angle is the largest at a finite AF filling ratio (fa=0.6), reaching 22.5°μm-1 and about 20 times that of FeF2. We also discuss the wave attenuation in the PCs, and consequently find that the attenuation is lower and the transmission is better in this geometry.

  1. Investigation of the chiral antiferromagnetic Heisenberg model using projected entangled pair states

    Science.gov (United States)

    Poilblanc, Didier

    2017-09-01

    A simple spin-1/2 frustrated antiferromagnetic Heisenberg model (AFHM) on the square lattice—including chiral plaquette cyclic terms—was argued [A. E. B. Nielsen, G. Sierra, and J. I. Cirac, Nat. Commun. 4, 2864 (2013), 10.1038/ncomms3864] to host a bosonic Kalmeyer-Laughlin (KL) fractional quantum Hall ground state [V. Kalmeyer and R. B. Laughlin, Phys. Rev. Lett. 59, 2095 (1987), 10.1103/PhysRevLett.59.2095]. Here, we construct generic families of chiral projected entangled pair states (chiral PEPS) with low bond dimension (D =3 ,4 ,5 ) which, upon optimization, provide better variational energies than the KL Ansatz. The optimal D =3 PEPS exhibits chiral edge modes described by the Wess-Zumino-Witten SU(2) 1 model, as expected for the KL spin liquid. However, we find evidence that, in contrast to the KL state, the PEPS spin liquids have power-law dimer-dimer correlations and exhibit a gossamer long-range tail in the spin-spin correlations. We conjecture that these features are genuine to local chiral AFHM on bipartite lattices.

  2. UA/ORNL Collaboration: Neutron Scattering Studies of Antiferromagnetic Films, Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Mankey, Gary J.

    2006-07-26

    The work reported here was a collaborative project between the research groups of Dr. J.L. Robertson at Oak Ridge National Laboratory and Dr. G.J. Mankey at the University of Alabama. The main thrust is developing neutron optical devices and materials for the study of magnetic thin films and interfaces. The project is particularly timely, since facility upgrades are currently underway at the High Flux Isotope Reactor. A new neutron optical device, a multicrystal analyzer, was designed and built to take maximum advantage of the increased flux that the upgraded beamlines at HFIR will provide. This will make possible detailed studies of the magnetic structure of thin films, multilayers, and interfaces that are not feasible at present. We performed studies of the antiferromagnetic order in thin films and crystals using neutron scattering, determined magnetic structures at interfaces with neutron reflectometry and measured order in magnetic dispersions using small angle neutron scattering. The collaboration has proved fruitful: generating eleven publications, contributing to the training of a postdoc who is now on staff at the High Flux Isotope Reactor and providing the primary support for two recent Ph.D. recipients. The collaboration is still vibrant, with anticipated implementation of the multicrystal analyzer on one of the new cold source beamlines at the High Flux Isotope Reactor.

  3. Competition between ferromagnetic and antiferromagnetic interactions by Cr doping at Mn sites in antiperovskite Mn{sub 3−x}Cr{sub x}ZnN (0≤x≤0.5) compounds

    Energy Technology Data Exchange (ETDEWEB)

    Malik, Muhammad Imran; Sun, Ying; Wang, Lei; Deng, Sihao; Shi, Kewen; Hu, Pengwei; Lu, Huiqing; Wang, Cong, E-mail: congwang@buaa.edu.cn

    2016-05-01

    The Cr doping effect on the lattice and magnetic properties in Mn{sub 3−x}Cr{sub x}ZnN was reported in the antiferromagnetic intermetallic host material Mn{sub 3}ZnN. The lattice parameter decreases with the increase of the Cr concentration. Measurements of magnetization from 10 K to 350 K reveal that sharp antiferromagnetic (AFM)-to-paramagnetic (PM) transitions of the host material exist at 185 K (ZFC) and 177 K (FC). The peak is broadened clearly as the Cr doping was increased and when the Cr concentration exceeded 0.3, a significant ferromagnetic (FM) character was found to coexist with an AFM phase. At x=0.4 and 0.5, the M–H curves exhibit small magnetic hysteresis loop, indicating the dominant FM interactions in these samples. Also, a positive value of Weiss Temperature (Θ{sub W}) at x=0.5 in H/M–T plot suggests that the FM interaction is dominant when the Cr doping increases.

  4. Competition between ferromagnetic and antiferromagnetic interactions by Cr doping at Mn sites in antiperovskite Mn3-xCrxZnN (0≤x≤0.5) compounds

    Science.gov (United States)

    Malik, Muhammad Imran; Sun, Ying; Wang, Lei; Deng, Sihao; Shi, Kewen; Hu, Pengwei; Lu, Huiqing; Wang, Cong

    2016-05-01

    The Cr doping effect on the lattice and magnetic properties in Mn3-xCrxZnN was reported in the antiferromagnetic intermetallic host material Mn3ZnN. The lattice parameter decreases with the increase of the Cr concentration. Measurements of magnetization from 10 K to 350 K reveal that sharp antiferromagnetic (AFM)-to-paramagnetic (PM) transitions of the host material exist at 185 K (ZFC) and 177 K (FC). The peak is broadened clearly as the Cr doping was increased and when the Cr concentration exceeded 0.3, a significant ferromagnetic (FM) character was found to coexist with an AFM phase. At x=0.4 and 0.5, the M-H curves exhibit small magnetic hysteresis loop, indicating the dominant FM interactions in these samples. Also, a positive value of Weiss Temperature (ΘW) at x=0.5 in H/M-T plot suggests that the FM interaction is dominant when the Cr doping increases.

  5. Effects of Inventory Bias on Landslide Susceptibility Calculations

    Science.gov (United States)

    Stanley, T. A.; Kirschbaum, D. B.

    2017-01-01

    Many landslide inventories are known to be biased, especially inventories for large regions such as Oregon's SLIDO or NASA's Global Landslide Catalog. These biases must affect the results of empirically derived susceptibility models to some degree. We evaluated the strength of the susceptibility model distortion from postulated biases by truncating an unbiased inventory. We generated a synthetic inventory from an existing landslide susceptibility map of Oregon, then removed landslides from this inventory to simulate the effects of reporting biases likely to affect inventories in this region, namely population and infrastructure effects. Logistic regression models were fitted to the modified inventories. Then the process of biasing a susceptibility model was repeated with SLIDO data. We evaluated each susceptibility model with qualitative and quantitative methods. Results suggest that the effects of landslide inventory bias on empirical models should not be ignored, even if those models are, in some cases, useful. We suggest fitting models in well-documented areas and extrapolating across the study region as a possible approach to modeling landslide susceptibility with heavily biased inventories.

  6. Effects of Inventory Bias on Landslide Susceptibility Calculations

    Science.gov (United States)

    Stanley, Thomas; Kirschbaum, Dalia B.

    2017-01-01

    Many landslide inventories are known to be biased, especially inventories for large regions such as Oregons SLIDO or NASAs Global Landslide Catalog. These biases must affect the results of empirically derived susceptibility models to some degree. We evaluated the strength of the susceptibility model distortion from postulated biases by truncating an unbiased inventory. We generated a synthetic inventory from an existing landslide susceptibility map of Oregon, then removed landslides from this inventory to simulate the effects of reporting biases likely to affect inventories in this region, namely population and infrastructure effects. Logistic regression models were fitted to the modified inventories. Then the process of biasing a susceptibility model was repeated with SLIDO data. We evaluated each susceptibility model with qualitative and quantitative methods. Results suggest that the effects of landslide inventory bias on empirical models should not be ignored, even if those models are, in some cases, useful. We suggest fitting models in well-documented areas and extrapolating across the study region as a possible approach to modelling landslide susceptibility with heavily biased inventories.

  7. Induced spin-triplet pairing in the coexistence state of antiferromagnetism and singlet superconductivity: Collective modes and microscopic properties

    Science.gov (United States)

    Almeida, D. E.; Fernandes, R. M.; Miranda, E.

    2017-07-01

    The close interplay between superconductivity and antiferromagnetism in several quantum materials can lead to the appearance of an unusual thermodynamic state in which both orders coexist microscopically, despite their competing nature. A hallmark of this coexistence state is the emergence of a spin-triplet superconducting gap component, called a π triplet, which is spatially modulated by the antiferromagnetic wave vector, reminiscent of a pair density wave. In this paper, we investigate the impact of these π -triplet degrees of freedom on the phase diagram of a system with competing antiferromagnetic and superconducting orders. Although we focus on a microscopic two-band model that has been widely employed in studies of iron pnictides, most of our results follow from a Ginzburg-Landau analysis, and as such should be applicable to other systems of interest, such as cuprates and heavy fermion materials. The Ginzburg-Landau functional reveals not only that the π -triplet gap amplitude couples trilinearly with the singlet gap amplitude and the staggered magnetization magnitude but also that the π -triplet d -vector couples linearly with the magnetization direction. While in the mean-field level this coupling forces the d -vector to align parallel or antiparallel to the magnetization, in the fluctuation regime it promotes two additional collective modes—a Goldstone mode related to the precession of the d -vector around the magnetization and a massive mode, related to the relative angle between the two vectors, which is nearly degenerate with a Leggett-like mode associated with the phase difference between the singlet and triplet gaps. We also investigate the impact of magnetic fluctuations on the superconducting-antiferromagnetic phase diagram, showing that due to their coupling with the π -triplet order parameter the coexistence region is enhanced. This effect stems from the fact that the π -triplet degrees of freedom promote an effective attraction between

  8. Susceptibility Genes in Thyroid Autoimmunity

    Directory of Open Access Journals (Sweden)

    Yoshiyuki Ban

    2005-01-01

    Full Text Available The autoimmune thyroid diseases (AITD are complex diseases which are caused by an interaction between susceptibility genes and environmental triggers. Genetic susceptibility in combination with external factors (e.g. dietary iodine is believed to initiate the autoimmune response to thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence on the development of AITD. Various techniques have been employed to identify the genes contributing to the etiology of AITD, including candidate gene analysis and whole genome screening. These studies have enabled the identification of several loci (genetic regions that are linked with AITD, and in some of these loci, putative AITD susceptibility genes have been identified. Some of these genes/loci are unique to Graves' disease (GD and Hashimoto's thyroiditis (HT and some are common to both the diseases, indicating that there is a shared genetic susceptibility to GD and HT. The putative GD and HT susceptibility genes include both immune modifying genes (e.g. HLA, CTLA-4 and thyroid specific genes (e.g. TSHR, Tg. Most likely, these loci interact and their interactions may influence disease phenotype and severity.

  9. Hypnosis, hypnotic suggestibility, memory, and involvement in films.

    Science.gov (United States)

    Maxwell, Reed; Lynn, Steven Jay; Condon, Liam

    2015-05-01

    Our research extends studies that have examined the relation between hypnotic suggestibility and experiential involvement and the role of an hypnotic induction in enhancing experiential involvement (e.g., absorption) in engaging tasks. Researchers have reported increased involvement in reading (Baum & Lynn, 1981) and music-listening (Snodgrass & Lynn, 1989) tasks during hypnosis. We predicted a similar effect for film viewing: greater experiential involvement in an emotional (The Champ) versus a non-emotional (Scenes of Toronto) film. We tested 121 participants who completed measures of absorption and trait dissociation and the Harvard Group Scale of Hypnotic Susceptibility and then viewed the two films after either an hypnotic induction or a non-hypnotic task (i.e., anagrams). Experiential involvement varied as a function of hypnotic suggestibility and film clip. Highly suggestible participants reported more state depersonalization than less suggestible participants, and depersonalization was associated with negative affect; however, we observed no significant correlation between hypnotic suggestibility and trait dissociation. Although hypnosis had no effect on memory commission or omission errors, contrary to the hypothesis that hypnosis facilitates absorption in emotionally engaging tasks, the emotional film was associated with more commission and omission errors compared with the non-emotional film. Copyright © 2014 Elsevier Inc. All rights reserved.

  10. Reinventing suggestion systems for continuous improvement

    NARCIS (Netherlands)

    Schuring, R.W.; Luijten, Harald

    2001-01-01

    This article reports an experiment to increase the effectiveness of a suggestion system by deliberately applying principles of the kaizen and performance management. Design rules for suggestion systems are derived from these theories. The suggestion system that resulted differs from traditional

  11. pitting corrosion susceptibility pitting corrosion susceptibility of aisi ...

    African Journals Online (AJOL)

    eobe

    Abstract. The susceptibility of austenitic (AISI 301) stainless steel to pitting corrosion was evaluated in sodium chloride. (NaCl) solutions ... AISI 301 steel suffers from pitting corrosion in all the investigated solutions. AISI 301 steel suffers from ..... [1] Ijeomah, M.N.C. Elements of Corrosion and Protection. Theory, Auto Century ...

  12. Magnetic Susceptability Measurements in Superconductors

    Science.gov (United States)

    Kim, Jason; Mallory, Kendall; Seim, Ryan

    2000-04-01

    A new undergraduate research facility in magnetic susceptability measurements on superconductors is being developed at the University of Northern Colorado. Initial data measurements of the magnetic susceptability of various superconductors will be presented. These measurements were obtained with a liquid helium/nitrogen dewar that was reassembled for use in this project. The cryostat consists of two separate dewars, the first of which contains liquid nitrogen, the second, liquid helium. The liquid nitrogen dewar is used to keep the helium bath from evaporating off too quickly. Data on the evaporation rates of the two liquids will also be presented.

  13. Correlation Theory of the Heisenberg Antiferromagnet and Ferromagnet: Dependence on Dimension, Field, and Temperature

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1984-01-01

    -phase approximation and is applicable to the quantum spin case for any dimension and temperature. The static susceptibilities and the excitation spectrum are calculated. Besides the spin-wave excitations a central peak is found which can be understood as coming from local longitudinal fluctuations. The results...

  14. Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of KxFe2-ySe2

    Science.gov (United States)

    Zhao, Jun; Cao, Huibo; Bourret-Courchesne, E.; Lee, D.-H.; Birgeneau, R. J.

    2012-12-01

    The recently discovered K-Fe-Se high-temperature superconductor has caused heated debate regarding the nature of its parent compound. Transport, angle-resolved photoemission spectroscopy, and STM measurements have suggested that its parent compound could be insulating, semiconducting, or even metallic [M. H. Fang, H.-D. Wang, C.-H. Dong, Z.-J. Li, C.-M. Feng, J. Chen, and H. Q. Yuan, Europhys. Lett. 94, 27009 (2011)EULEEJ0295-507510.1209/0295-5075/94/27009; F. Chen , Phys. Rev. X 1, 021020 (2011)PRXHAE2160-330810.1103/PhysRevX.1.021020; and W. Li , Phys. Rev. Lett. 109, 057003 (2012)PRLTAO0031-900710.1103/PhysRevLett.109.057003]. Because the magnetic ground states associated with these different phases have not yet been identified and the relationship between magnetism and superconductivity is not fully understood, the real parent compound of this system remains elusive. Here, we report neutron-diffraction experiments that reveal a semiconducting antiferromagnetic (AFM) phase with rhombus iron vacancy order. The magnetic order of the semiconducting phase is the same as the stripe AFM order of the iron pnictide parent compounds. Moreover, while the 5×5 block AFM phase coexists with superconductivity, the stripe AFM order is suppressed by it. This leads us to conjecture that the new semiconducting magnetic ordered phase is the true parent phase of this superconductor.

  15. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y. -D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-16

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  16. Thermal Transport and Magnetotransport Properties of CuCr1-xMgxO2 with a Spin-3/2 Antiferromagnetic Triangular Lattice

    Science.gov (United States)

    Okuda, Tetsuji; Oozono, Satoshi; Kihara, Takumi; Tokunaga, Masashi

    2013-01-01

    We have investigated the thermal conductivity (κ) and magnetoresistance (MR) of non-doped and hole-doped delafossite CuCrO2 with a spin-3/2 antiferromagnetic (AF) triangular sublattice. The phonon mean free path above the Néel temperature (TN) deduced from κ and lattice specific heat is almost identical to the magnetic correlation length, which indicates that, for both compounds, spin fluctuation enhanced in a geometrically frustrated lattice is strongly coupled with acoustic phonon above TN. κ below TN is significantly suppressed by Mg substitution, suggesting the introduction of some disorder into the 120° Néel state. For the hole-doped CuCr0.97Mg0.03O2, a negative MR is observed above TN, which is enhanced with a decrease in T toward TN, while a component of positive MR appears below TN and the residual negative MR component is observed in a high magnetic field, indicating that spin fluctuation coupled with electrical conductivity is critically enhanced above TN and remains below TN. These results evidence that the 120° Néel state is partially disordered by a doped itinerant hole coupled with spin fluctuation, although AF transition is certainly promoted. The dynamic partial disorder may stabilize the Néel order through an order-by-disorder mechanism.

  17. Nonmagnetic impurities and roughness effects on the finite temperature magnetic properties of core-shell spherical nanoparticles with antiferromagnetic interface coupling

    Science.gov (United States)

    Vatansever, Erol; Yüksel, Yusuf

    2017-11-01

    Being inspired by a recent study (Dimitriadis et al., 2015), we study the finite temperature magnetic properties of the spherical nanoparticles with antiferromagnetic interface coupling including quenched (i) surface and (ii) interface nonmagnetic impurities (static holes) as well as (iii) roughened interface effects. The particle core is composed of ferromagnetic spins, and it is surrounded by a ferromagnetic shell. By means of Monte Carlo simulation based on an improved Metropolis algorithm, we implement the nanoparticles using classical Heisenberg Hamiltonians. Particular attention has also been devoted to elucidate the effects of the particle size on the thermal and magnetic phase transition features of these systems. For nanoparticles with imperfect surface layers, it is found that bigger particles exhibit lower compensation point which decreases gradually with increasing amount of vacancies, and vanishes at a critical value. In view of nanoparticles with diluted interface, our Monte Carlo simulation results suggest that there exists a region in the disorder spectrum where compensation temperature linearly decreases with decreasing dilution parameter. For nanoparticles with roughened interface, it is observed that the degree of roughness does not play any significant role on the variation of both the compensation point and critical temperature. However, the low temperature saturation magnetizations of the core and shell interface regions sensitively depend on the roughness parameter.

  18. The appearance of homogeneous antiferromagnetism in URu sub 2 Si sub 2 under high pressure: a sup 2 sup 9 Si nuclear magnetic resonance study

    CERN Document Server

    Matsuda, K; Kohara, T; Amitsuka, H; Kuwahara, K; Matsumoto, T

    2003-01-01

    We have investigated the low-temperature phase appearing below T sub o = 17.5 K in URu sub 2 Si sub 2 by means of sup 2 sup 9 Si nuclear magnetic resonance (NMR) in a pressure range from 0 to 17.5 kbar across the pressure-induced phase transition at P sub c = 15 kbar. At pressures below P sub c , we have observed the sup 2 sup 9 Si NMR lines arising from antiferromagnetic (AF) and paramagnetic (PM) regions in the sample, giving evidence for a phase-separated AF ordering below T sub o. The AF region increases in volume fraction with increasing pressure up to P sub c. In the PM region, the temperature-dependence of the nuclear spin-lattice relaxation rate at Si sites shows a rapid decrease below T sub o , strongly suggesting the occurrence of a phase transition driven by a hidden order parameter. As applied pressure exceeds P sub c , the AF ordering appears uniformly at T sub o throughout the sample. In the pressure range from 0 to 17.5 kbar, the magnitude of the internal field at Si sites in the AF region rema...

  19. Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-x D x.

    Science.gov (United States)

    Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C; Otomo, Toshiya; Hosono, Hideo

    2017-05-30

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1-x D x , and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

  20. Observation of antiferromagnetic correlations in the Hubbard model with ultracold atoms.

    Science.gov (United States)

    Hart, Russell A; Duarte, Pedro M; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T; Trivedi, Nandini; Huse, David A; Hulet, Randall G

    2015-03-12

    Ultracold atoms in optical lattices have great potential to contribute to a better understanding of some of the most important issues in many-body physics, such as high-temperature superconductivity. The Hubbard model--a simplified representation of fermions moving on a periodic lattice--is thought to describe the essential details of copper oxide superconductivity. This model describes many of the features shared by the copper oxides, including an interaction-driven Mott insulating state and an antiferromagnetic (AFM) state. Optical lattices filled with a two-spin-component Fermi gas of ultracold atoms can faithfully realize the Hubbard model with readily tunable parameters, and thus provide a platform for the systematic exploration of its phase diagram. Realization of strongly correlated phases, however, has been hindered by the need to cool the atoms to temperatures as low as the magnetic exchange energy, and also by the lack of reliable thermometry. Here we demonstrate spin-sensitive Bragg scattering of light to measure AFM spin correlations in a realization of the three-dimensional Hubbard model at temperatures down to 1.4 times that of the AFM phase transition. This temperature regime is beyond the range of validity of a simple high-temperature series expansion, which brings our experiment close to the limit of the capabilities of current numerical techniques, particularly at metallic densities. We reach these low temperatures using a compensated optical lattice technique, in which the confinement of each lattice beam is compensated by a blue-detuned laser beam. The temperature of the atoms in the lattice is deduced by comparing the light scattering to determinant quantum Monte Carlo simulations and numerical linked-cluster expansion calculations. Further refinement of the compensated lattice may produce even lower temperatures which, along with light scattering thermometry, would open avenues for producing and characterizing other novel quantum states of

  1. Topological Many-Body States in Quantum Antiferromagnets via Fuzzy Supergeometry

    Directory of Open Access Journals (Sweden)

    Keisuke Totsuka

    2013-04-01

    Full Text Available Recent vigorous investigations of topological order have not only discovered new topological states of matter, but also shed new light on “already known” topological states. One established example with topological order is the valence bond solid (VBS states in quantum antiferromagnets. The VBS states are disordered spin liquids with no spontaneous symmetry breaking, but most typically manifest a topological order known as a hidden string order on the 1D chain. Interestingly, the VBS models are based on mathematics analogous to fuzzy geometry. We review applications of the mathematics of fuzzy supergeometry in the construction of supersymmetric versions of VBS (SVBS states and give a pedagogical introduction of SVBS models and their properties. As concrete examples, we present detailed analysis of supersymmetric versions of SU(2 and SO(5 VBS states, i.e., UOSp(N|2 and UOSp(N|4 SVBS states, whose mathematics are closely related to fuzzy two- and four-superspheres. The SVBS states are physically interpreted as hole-doped VBS states with a superconducting property that interpolates various VBS states, depending on the value of a hole-doping parameter. The parent Hamiltonians for SVBS states are explicitly constructed, and their gapped excitations are derived within the single-mode approximation on 1D SVBS chains. Prominent features of the SVBS chains are discussed in detail, such as a generalized string order parameter and entanglement spectra. It is realized that the entanglement spectra are at least doubly degenerate, regardless of the parity of bulk (superspins. The stability of the topological phase with supersymmetry is discussed, with emphasis on its relation to particular edge (superspin states.

  2. Critical behavior of an anisotropic Ising antiferromagnet in both external longitudinal and transverse fields

    Energy Technology Data Exchange (ETDEWEB)

    Nascimento, Denise A. do, E-mail: denise.a.n@bol.com.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus-AM (Brazil); Departamento de Fisica, Universidade Federal de Roraima, BR 174, Km 12. Bairro Monte Cristo, CEP: 69300-000 Boa Vista/RR (Brazil); Neto, Minos A., E-mail: minosneto@hotmail.com [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus-AM (Brazil); Ricardo de Sousa, J., E-mail: jsousa@edu.ufam.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus-AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, 69077-000 Manaus-AM (Brazil); Pacobahyba, Josefa T., E-mail: jtmpacobahyba@dfis.ufrr.br [Departamento de Fisica, Universidade Federal de Roraima, BR 174, Km 12. Bairro Monte Cristo, CEP: 69300-000 Boa Vista/RR (Brazil)

    2012-08-15

    In this paper we study the critical behavior of a two-sublattice Ising model on an anisotropic square lattice in both uniform longitudinal (H) and transverse ({Omega}) fields by using the effective-field theory. The model consists of ferromagnetic interaction J{sub x} in the x direction and antiferromagnetic interaction J{sub y} in the y direction in the presence of the H and {Omega} fields. We obtain the phase diagrams in the H-T and {Omega}-T planes changing values of the {Omega} and H parameters, respectively for fixed value at {lambda}=J{sub x}/J{sub y}=1. At null temperature, the ground state phase diagram in the {Omega}-H plane for several values of {lambda} parameter is analyzed. In the particular case of {lambda}=1 we compare our results with mean-field theory (MFT) and was not observed reentrant behavior around of the critical field H{sub c}/J{sub y}=2.0 for {Omega}=0 by using EFT. - Highlights: Black-Right-Pointing-Pointer In the last decade there has been a great interest in physics of the quantum phase transition in system at low dimensional. Black-Right-Pointing-Pointer In particular, the transverse Ising model has been studied by a variety of approximate methods. Black-Right-Pointing-Pointer In the context of quantum phase transition and critical phenomena. Black-Right-Pointing-Pointer First time, is presented a study of the superantiferromagnetic transverse Ising model on an anisotropic square lattice. Black-Right-Pointing-Pointer We have obtained finite temperature and ground state phase diagrams.

  3. Itinerant spin dynamics in iron-based superconductors and cerium-based heavy-fermion antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Friemel, Gerd

    2014-05-26

    This thesis contains a comprehensive study of the spin excitations by inelastic neutron scattering (INS) in two different correlated electron systems: the alkali-metal iron selenide superconductors (FeSe122) A{sub x}Fe{sub 2-y}Se{sub 2} (A=K, Rb, Cs) and the heavy-fermion antiferromagnet CeB6. Both systems exhibit intense modes in their spin-fluctuation spectrum below their respective transition temperatures that can be derived from the spin dynamics of the itinerant quasiparticles. However, the implications of these observations, presented here, are different for each particular compound. The A{sub x}Fe{sub 2-y}Se{sub 2} superconductors, with a uniform T{sub c} of 32 K, belong to a qualitative new family of superconductors. They possess a distinctly different Fermi surface compared to the iron-arsenide-based analogues XFe{sub 2}As{sub 2} (X=Ca, Sr, Ba). Instead of the central hole pockets at Γ and the electron pockets at X((1)/(2) 0), which are nested by the Q{sub AFM} = ((1)/(2) 0) vector, there exist only large electron pockets at the X point. Therefore, the magnetic instability along Q{sub AFM} that presumably provides the pairing glue for the superconductivity in the shape of spin fluctuations is absent in the FeSe122. The search for spin fluctuations by INS was motivated by a theoretical analysis that predicted their presence at an incommensurate wave vector near Q = (0.5 δ), δ = 0.3125 which results from a quasinesting by Q between the flat parts of the electron pockets. Two samples, namely Rb{sub 0.8}Fe{sub 1.6}Se{sub 2} and K{sub 0.77}Fe{sub 1.85}Se{sub 2}, were prepared and both showed a sizable anisotropic magnetic response at Q{sub sf} = ((1)/(2) (1)/(4)) in the normal state. Furthermore, upon entering the superconducting (SC) state a strong excitation appears at ℎω{sub res} = 14 meV in the spectrum at Q{sub sf}, which is referred to as magnetic resonant mode. This mode is interpreted as a bound spin-1 exciton below the SC charge gap. Its presence

  4. Topological susceptibility from the overlap

    DEFF Research Database (Denmark)

    Del Debbio, Luigi; Pica, Claudio

    2003-01-01

    The chiral symmetry at finite lattice spacing of Ginsparg-Wilson fermionic actions constrains the renormalization of the lattice operators; in particular, the topological susceptibility does not require any renormalization, when using a fermionic estimator to define the topological charge. Theref...

  5. Hypnotic suggestion: opportunities for cognitive neuroscience.

    Science.gov (United States)

    Oakley, David A; Halligan, Peter W

    2013-08-01

    Hypnosis uses the powerful effects of attention and suggestion to produce, modify and enhance a broad range of subjectively compelling experiences and behaviours. For more than a century, hypnotic suggestion has been used successfully as an adjunctive procedure to treat a wide range of clinical conditions. More recently, hypnosis has attracted a growing interest from a cognitive neuroscience perspective. Recent studies using hypnotic suggestion show how manipulating subjective awareness in the laboratory can provide insights into brain mechanisms involved in attention, motor control, pain perception, beliefs and volition. Moreover, they indicate that hypnotic suggestion can create informative analogues of clinical conditions that may be useful for understanding these conditions and their treatments.

  6. Estimation of the Population Susceptibility Against Measles in Slovakia.

    Science.gov (United States)

    Zibolenová, Jana; Chladná, Zuzana; Švihrová, Viera; Baška, Tibor; Waczulíková, Iveta; Hudečková, Henrieta

    2017-03-01

    In Slovakia, thanks to a highly effective vaccination programme, no domestic cases of measles have been reported since 1999. However, there are several outbreaks of measles currently hitting some countries in Europe. Difficulties in reaching the goal of measles elimination make it necessary to monitor the status of the population susceptibility to prevent similar outbreaks in the future. We hypothesize that immunity wanes overtime, which can substantially impact the population susceptibility. This work introduces a model that estimates a proportion of individuals susceptible to measles in the Slovak population in 2015. Our analysis is based on an age-cohort model that incorporates waning immunity, vaccination schedule and changes in demographic structure. The inputs of the model are data on the vaccination coverage, last seroprevalence survey in 2002 and age structure of the population. In a short-term horizon, waning immunity does not affect the estimated proportion of the susceptible population. However, in a long-term horizon, the antibody titers can fall below the level of protection, which would result in a substantial transfer of initially immune individuals to the compartment of the susceptible ones. Incorporating of waning immunity in the cohort model has indicated that the most susceptible cohorts are not-vaccinated youngest children and cohorts born between 1969 and 1986. Applying the model to the current situation shows that people aged 30-45 years and unvaccinated infants represent the most susceptible groups. Model partially replaces missing seroprevalence survey, but, because the parameters of model and phenomenon of waning immunity are not exactly known, we suggest reintroducing the regular national serosurveys in order to empirically determine the level of susceptibility for measles in Slovakia.

  7. Maltreated Children's Memory: Accuracy, Suggestibility, and Psychopathology

    Science.gov (United States)

    Eisen, Mitchell L.; Goodman, Gail S.; Qin, Jianjian; Davis, Suzanne; Crayton, John

    2007-01-01

    Memory, suggestibility, stress arousal, and trauma-related psychopathology were examined in 328 3- to 16-year-olds involved in forensic investigations of abuse and neglect. Children's memory and suggestibility were assessed for a medical examination and venipuncture. Being older and scoring higher in cognitive functioning were related to fewer…

  8. Query term suggestion in academic search

    NARCIS (Netherlands)

    Verberne, S.; Sappelli, M.; Kraaij, W.

    2014-01-01

    In this paper, we evaluate query term suggestion in the context of academic professional search. Our overall goal is to support scientists in their information seeking tasks. We set up an interactive search system in which terms are extracted from clicked documents and suggested to the user before

  9. Electrocardiographic features suggestive of a left. ventricular ...

    African Journals Online (AJOL)

    SA MEDICAL JOURNAL VOLUME 63 1 JANUARY 1983. 27. Electrocardiographic features suggestive of a left. ventricular' aneurysm following a high-velocity missile injury. A case report. T. H. DIAMOND, R. SMITH, D. P. MYBURGH, L. STEINGO. Summary. Electrocardiographic features suggestive of a transmural anterior ...

  10. Are there stress resistant and susceptible myocardia?

    Science.gov (United States)

    Knight, V A

    1988-11-01

    The satisfactory analysis of the Na/K ATPase, its pumping component and the mechanism of action of the inhibitor digitalis remains elusive; yet the controversial inotropic effect of digitalis in the clinical setting has been known for over a century. There are also conflicting reports of the effect of urea and uremia on the cardiovascular system, and the evidence as it exists, suggests that urea may have two effects on the intact heart, by virtue of its extent of action on hydrogen bonding of water molecules, determined by which type of muscle constitutes the myocardium. If different types of myocardium do exist, they could well respond differently to inotropic agents. Evidence suggests that two types of myocardia, relatively stress resistant or susceptible may exist, analagous to known skeletal muscle differences.

  11. Diamagnetic susceptibility obtained from the six-vertex model and its implications for the high-temperature diamagnetic state of cuprate superconductors.

    Science.gov (United States)

    Sau, Jay D; Tewari, Sumanta

    2011-10-21

    We study the diamagnetism of the six-vertex model with the arrows as directed bond currents. To our knowledge, this is the first study of the diamagnetism of this model. A special version of this model, called the F model, describes the thermal disordering transition of an orbital antiferromagnet, known as d-density wave, a proposed state for the pseudogap phase of the high-T(c) cuprates. We find that the F model is strongly diamagnetic and the susceptibility may diverge in the high-temperature critical phase with power-law arrow correlations. These results may explain the surprising recent observation of a diverging low-field diamagnetic susceptibility seen in some optimally doped cuprates within the d-density wave model of the pseudogap phase. © 2011 American Physical Society

  12. Critical behavior of the three-dimensional Heisenberg antiferromagnet RbMnF3

    DEFF Research Database (Denmark)

    Coldea, R.; Cowley, R.A.; Perring, T.G.

    1998-01-01

    . In agreement with previous measurements, at T-N and for wave vectors away from the AF zone center, the scattering has a quasielastic component in addition to the inelastic response predicted by renormalization-group and mode-coupling theories. Both components scale with the dynamic exponent z = 1.43 +/- 0.......04, in agreement with dynamic scaling. On cooling below T-N the inelastic peaks transform into the transverse spin waves and a crossover has been observed in the dispersion from a power-law relation omega(q) = Aq(z) at T-N to a linear behavior omega(q) = cq in the hydrodynamic region below T-N. The quasielastic...... component evolves below T-N into the longitudinal susceptibility identified in an earlier polarized neutron experiment. The intensity and energy width of the longitudinal scattering decrease on cooling below T-N. Down to the lowest temperatures where the longitudinal susceptibility could be measured...

  13. Quasi-1D s=1/2 antiferromagnet Cs2CuCl4 in a magnetic field

    DEFF Research Database (Denmark)

    Coldea, R.; Tennant, D.A.; Cowley, R.A.

    1997-01-01

    Magnetic excitations of the quasi-1D S = 1/2 Heisenberg antiferromagnet (HAF) Cs2CuCl4 have beer measured as a function of magnetic field using neutron scattering. For T Fields greater than B-c = 1.66 T, but less...... than the field (similar or equal to 8 T) required to fully align the spins, are observed to decouple the chains, and the system enters a disordered intermediate-field phase (IFP). The IFP excitations are in agreement with the predictions of Muller et al. for the 1D S = 1/2 HAF, and Talstra and Haldane...

  14. Algebraic vortex liquid in spin-1/2 triangular antiferromagnets: Scenario for Cs_2CuCl_4

    OpenAIRE

    Alicea, Jason; Motrunich, Olexei I.; Fisher, Matthew P. A.

    2005-01-01

    Motivated by inelastic neutron scattering data on Cs_2CuCl_4, we explore spin-1/2 triangular lattice antiferromagnets with both spatial and easy-plane exchange anisotropies, the latter due to an observed Dzyaloshinskii-Moriya interaction. Exploiting a duality mapping followed by a fermionization of the dual vortex degrees of freedom, we find a novel "critical" spin-liquid phase described in terms of Dirac fermions with an emergent global SU(4) symmetry minimally coupled to a non-compact U(1) ...

  15. Reply to ``Comment on `Magnetic field effects on neutron diffraction in the antiferromagnetic phase of $UPt_3$'''

    OpenAIRE

    Moreno, Juana; Sauls, J A

    2002-01-01

    Fak, van Dijk and Wills (FDW) question our interpretation of elastic neutron-scattering experiments in the antiferromagnetic phase of UPt_3. They state that our analysis is incorrect because we average over magnetic structures that are disallowed by symmetry. We disagree with FDW and reply to their criticism. FDW also point out that we have mistaken the magnetic field direction in the experiment reported by N. H. van Dijk et al. [Phys. Rev. B 58, 3186 (1998)]. We correct this error and note t...

  16. Competition among Superconducting, Antiferromagnetic, and Charge Orders with Intervention by Phase Separation in the 2D Holstein-Hubbard Model

    Science.gov (United States)

    Ohgoe, Takahiro; Imada, Masatoshi

    2017-11-01

    Using a variational Monte Carlo method, we study the competition of strong electron-electron and electron-phonon interactions in the ground state of the Holstein-Hubbard model on a square lattice. At half filling, an extended intermediate metallic or weakly superconducting (SC) phase emerges, sandwiched between antiferromagnetic and charge order (CO) insulating phases. By carrier doping into the CO insulator, the SC order dramatically increases for strong electron-phonon couplings, but is largely hampered by wide phase separation (PS) regions. Superconductivity is optimized at the border to the PS.

  17. Magnetic correlations in the 2D S=5/2 honeycomb antiferromagnet MnPS3

    DEFF Research Database (Denmark)

    Rønnow, H.M.; Wildes, A.R.; Bramwell, S.T.

    2000-01-01

    MnPS3 is a quasi-2D S = 5/2 antiferromagnet on a honeycomb lattice. Using an energy integrating neutron scattering technique, we have measured the structure factor S(k) of the instantaneous magnetic fluctuations. The temperature dependence of the correlation length xi follows the Kosterlitz-Thoul......-Thouless prediction with parameters that are consistently described by a Heisenberg system with inter plane coupling J'/'J = 1/405 and weak xy-anisotropy. (C) 2000 Elsevier Science B.V. All rights reserved....

  18. Initialization of unidirectional anisotropy in a ferromagnet-antiferromagnet bilayer by keV-He ion bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Engel, D. [Fachbereich Physik, Technische Universitaet Kaiserslautern, Erwin-Schroedinger-Str. D-67663 Kaiserslautern (Germany)]. E-mail: wengel@rhrk.uni-kl.de; Ehresmann, A. [Fachbereich Physik, Technische Universitaet Kaiserslautern, Erwin-Schroedinger-Str. D-67663 Kaiserslautern (Germany); Schmalhorst, J. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33501 Bielefeld (Germany); Sacher, M. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33501 Bielefeld (Germany); Hoeink, V. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33501 Bielefeld (Germany); Reiss, G. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33501 Bielefeld (Germany)

    2005-06-15

    A polycrystalline Cu/Ni{sub 80}Fe{sub 20}/Mn{sub 83}Ir{sub 17}/Co/AlO{sub x} ferromagnet-antiferromagnet layer system grown without applying an external magnetic field shows no unidirectional anisotropy in the as-prepared state. After 10keV-He ion bombardment in an external in-plane magnetic field, a clear unidirectional anisotropy collinear to the magnetic field direction during bombardment is observed, indicating that ion bombardment can be used for this system to initialize the unidirectional exchange anisotropy. The magnetization reversal processes for various ion doses are discussed, based on longitudinal magnetooptical Kerr-effect measurements.

  19. Magnetic susceptibility as a biosignature in stromatolites

    Science.gov (United States)

    Petryshyn, Victoria A.; Corsetti, Frank A.; Frantz, Carie M.; Lund, Steve P.; Berelson, William M.

    2016-03-01

    results. The results of these experiments suggest that magnetic susceptibility shows promise as a new biosignature in the study of putative microbialites.

  20. Electrocardiographic features suggestive of a left. ventricular ...

    African Journals Online (AJOL)

    Abstract. Electrocardiographic features suggestive of a transmural anterior myocardial infarction with resultant left ventricular aneurysm formation were found in a 22-year-old man who had sustained a ballistic missile injury to his chest.